Updated December 22, 1999 THE COMPLETE JAGUAR BATTERY CARE PROGRAM Dec, 1999 I am 67 years old.For some 56 of those years, I have been “into” batteries, and thought I knew just about all there was to know about them.
Then, in 1995, I bought a 1992 Jaguar XJ-40 that was, and is, in mint condition. It is “Silver” with blue leather interior.
When I looked into the “owner’s packet,” I found a large card stating: “CAUTION: To prevent a dead battery, disconnect prior to leaving the vehicle parked for extended periods.* (*2 to 3 weeks, depending on the state of charge at the time the vehicle is left)”
I said: “Whoa! That’s a pretty short time, and they’re talking DEAD battery!”
Then I read the “Owner’s Manual” and found the following three interesting statements:
First, “The service life of the battery is also dependent on its condition of charge.”
Second, “It must always be sufficiently charged for the battery to last an optimum length of time.”
Third, “Therefore, we recommend that the battery charge is checked frequently if the vehicle is used mostly for short distance trips, or if it is not used for long periods of time.”
Then, when reading the technical information about the new XJ-8, I found this intriguing statement:
“Multiplexed electronics system modules have a “sleep” mode to reduce battery drain.”
AND, then I came across a Service Bulletin from Jaguar to it’s dealers warning them about customer problems from selling cars with undercharged batteries and explaining the need for frequent charges to keep them in shape.
SHAZAM! Said I, hand hitting forehead. That’s the reason I see so many “battery” problems on the JagLovers net.OK, so what to do? Well, first, devise a “plan” that will neutralize this built-in problem, and, second, write it up so others can see what to do and why they should do it. So, here we go!
This paper is based on three premises:
First that there is absolutely nothing good about a poor battery.
The basis for our car’s entire existence is electrical, and a failure may place us in physical and/or financial danger.
Murphy’s Law will dictate that the failure will happen at the worst possible place. It may cost a tow or a meeting missed, and a new battery purchased on the road may well cost twice what it should IF one can be found.
If we choose to “Jump” the battery, we place both our alternator and on-board computers in jeopardy. In short, living with a “bum” battery is risking a disaster.
Second, that the XJ-40 on-board electronic system can be pretty tough on batteries.
And, third, that we can, with just a little bit of intelligent effort, stay ahead of the Cat, and ensure that we NEVER (well, almost never) suffer a battery problem.
Equipment needed:
o Battery hydrometer (NA for sealed battery)
o Hand-held digital voltmeter
o Small (1/2 to one amp) non-automatic charger
DETAILS
(In the beginning - new battery, new car, or beginning this maintenance plan with an old one)
I. With the Battery on the bench - (if possible, in car less desirable)
A) Wash the battery case with soda water (teaspoon of baking soda in a glass of warm water), then rinse it and let it dry
B) Clean the battery terminals (bright and shiny clean!)
C) Document the characteristics of THIS battery.
1) Charge slowly (2 amps max) until both voltage and specific gravity (SG) stabilize. (This could take several days) Note: I am responsible for four batteries.
Their final, stabilized voltage on my 1/2 amp charger is 15.32, 15.38, 15.46 and 15.99. As you see, each one is unique.
2) Record the above values two ways -
On charge - A) Specific Gravity_________
B) Voltage________ Off charge - (a day or so later) - Voltage________(SG will be the same)
Note: This initial charging is absolutely vital to ensure that your battery gets started right.
I have confirmed that “new” batteries have been on the shelf for up to 6 months, may be more than half discharged, AND already sulfated.
In June, 1998, I found this battery condition in my Sister’s brand new SUV.
In November, 1999, I checked at least ten batteries at each of three stores and found: none fully charged, most between 3/4 and 1/2 charged and one dead.
II. Install the battery in the carA) Dip the cable ends in soda water to neutralize any acid on them, dry, make the connecting surfaces bright and shiny, then cover them with a light coating of non-metallic grease (Vaseline is fine). Connect the positive (+) cable first, then the negative (-) cable.
B) Calibrate the in-dash voltmeter by comparing with simultaneous readings at the battery with the digital voltmeter. Note and record any difference as a constant.
III. Test the battery/ alternator combination -
A) Start the car, wait until the voltmeter reaches it’s highest value, then, with the digital voltmeter, record the voltage at the battery_______. This is setting of the voltage regulator in your car. (It will be between 13.8 and 14.8, and is not adjustable)
B) Using the in-car voltmeter, test the load-carrying capacity of your alternator (so that later, you will be able to tell if something is going wrong)
1) After step A) above, note the voltage with the engine running slightly above idle (1,000 RPM is enough) and with all loads off.
2) Drop engine speed to idle and place transmission in a drive gear so the RPM is pulled down to 550-600 RPM. (The voltage should not change)
3) Turn on electrical loads one-at-a-time and observe the voltage change. (Add radio, headlights, low beam, high beam, heater blower to high, then rear window defroster) (The voltage will drop slightly as each load is added, but should stay above 13 until the rear window defroster is turned on - then it will probably slowly move down to near “battery” voltage - below 13)
4) Increase the engine speed (1,000 +-) and observe that the voltage rises to above 13.
5) Turn off the power consumers. Note: If the values on this first test are not close to the above, you may have a problem even now.
Several things should be noted about this test.
First, it shows that even a perfect alternator cannot carry the full load with the engine at a slow idle - so it is possible for the battery to be discharged while the engine is running.
(See the article “DEAD BATTERY BUT NOTHING WRONG” that was written for the January ‘95 SUBURBAN INSIDER - at the end of this article)
Second, it’s normal for system voltage to go down when carrying a load.
Third, it shows you how your system operates when it is in good condition.
If you develop a system defect, such as a slipping belt or a failed diode in the alternator, the voltage will drop under a much smaller load, thereby alerting you to the problem - BUT ONLY IF you are paying attention.
Recently a friend called me after stalling away from home. I asked what her voltmeter was reading, and found that she didn’t know she had one, or what it should read.
The alternator had failed!
IV. Daily (See Para # IX)
1) Turn the key to “on” and note the voltage reading (light-load battery voltage)
2) Note the voltage reading while the starter is cranking the engine (Heavy-load battery voltage - if lower than usual it’s a sure sign of a battery problem)
3) Note the voltage rise after the engine starts (regulated, alternator produced voltage)
4) Occasionally check the voltage value. From it’s high, it will drop from .5 to 1.0 volts as the underhood temp rises.
5) Check the voltage frequently as you drive. If it drops to or below “battery voltage” -- the number you had at step #1 above, you have had an alternator failure. **
Here is where a “good” battery pays off -- turn off all power consumers, and it will carry you to safety.
A “bad” battery might stall you almost immediately.
V. Monthly (This procedure is your BEST ASSURANCE of maintaining a good battery)
1) Test the battery’s “Off charge” SG and/or voltage.
2) If not very close to the original values, charge slowly (with the same little charger as before) until the SG equals the original value and the “on charge” voltage peaks and stabilizes. (But charge at least overnight once every month)
3) Check to see that corrosion is not appearing on the connectors, and that the battery top does not look “wet” (acid). If “Yes” on either, correct it.
VI. Occasionally 1) Do the alternator “proof test” (para # III. B) to ensure that the charging system is healthy.
VII. Annually (In addition to the regular monthly service)
1) Check electrolyte level and carefully (with the hydrometer) add distilled water as needed. It should take only a small (1/3 hydrometer per cell) amount.
** Do not “fill” the cells. High water usage is a major warning sign of trouble.
2) Unless the battery top appears totally dry, wipe it with a cloth dipped in the soda/water solution. If the area “fizzes,” it had acid on it. (Acid will speed the loss of charge.)
3) Remove and clean (shiny) the connectors and renew the light coating of non-metallic grease. (Check radio security code and frequencies first)
VIII. When the battery reaches it’s “guaranteed life”
1) Watch for battery sales and BUY A NEW ONE (Remember - buy the best)
2) Bring the battery home and start “The Plan” over again. (Para I A) above )
It is likely that the specifics on the new battery will be somewhat different than for the old one.
3) Put the old one on the shelf and give it regular maintenance - just as if it was in the car.
4) Use this battery as a loaner, as a spare, or as the trade-in next time. (I take mine with me if I’m going out in the remote backwoods - just in case)
IX.NORMAL OPERATION
Beginning with a good battery that is fully charged, the normal sequence of daily electrical events is:
A) Key on - ignition, brake boost pressure pump, heater fan and interior lights are all operating. The load on the battery will be less than 25 amps, so the voltage will be pulled down slightly from the basic “no load” value. (Which is about 12.8 when fully charged)
B) Cranking engine - in addition to the above loads, the starter will require some 200 to 300 amps, so the battery voltage will drop to the 9 to 10V range.
C) When the engine starts, the alternator begins to generate power. The voltage regulator will sense that the system voltage is down because of the power used in the starting operation, and produce a high amperage output. The voltage will quickly move up to a position just below the “running” voltage, then, in a matter of seconds, when the lost power is restored to the battery, the voltage will move up to it’s highest value.
D) As radio and lights are turned on, the voltage will drop ever so slightly as the alternator picks up this additional load.
E) Later, as you drive, the underhood temperature rises, and the voltage will move down a small amount - between 0.5 and 1.0 volt.
Second section ---
X. BATTERY/ CHARGING SYSTEMS - A HISTORY
A) THE AMPS BASED SYSTEM.
Back when Charles Kettering, of General Motors, invented the self-starter, the only instruments in the panel were an ammeter and a speedometer. The electrical loads on most cars consisted of the starter and lights. Drivers got used to seeing the ammeter needle on the plus side of the zero, and found that if it wasn’t, they soon had a dead battery. Generator output was determined by the setting of a 3rd brush in the generator, and was a constant. This set amperage was forced into the battery without regard for it’s state of charge. (The light switch incorporated the clever provision of increasing the generator’s output to support the lights when they were on.)
Therefore, if the generator was set at a low rate for highway driving, the battery would run down when driving around town. If it was set at a higher rate for town driving, the battery would soon be destroyed by overcharging if used on the highway. The only true “regulator” was the electrolyte in the battery that was “boiled” away during overcharging.
And, overcharging was a way of life - some 62% of failures were due to it.
Battery failure was usually sudden, and was caused by the build-up of lead particles being sluffed off the plates by the violent bubbling action, which is the hallmark of overcharging. When the lead sediment built up to the bottom of the plates, the cell was shorted, and the battery went dead. Of course that lead sediment represented a loss of battery capacity as it was building up.
Look at it this way. Lets compare a battery to a bucket of water. Amperes represent a measure of the flow of current, so, amps flowing into a battery are similar to water flowing into a bucket.
If more water is being taken out than is flowing in, the water level (and pressure at the surface) drops. When more water comes in than goes out, the bucket simply overflows (pressure is limited) and the water runs elsewhere. In this system, when the battery was fully charged, the “overflow” amps spent their energy in disassociating water into hydrogen and oxygen gasses. (thereby creating an explosive mixture)
This “overflow” would drive the battery voltage up, and light bulbs, like batteries, tended to burn out rather quickly. Jaguar, in typically British understatement, simply directs: “If a high-speed charger is used, then the battery must be completely removed from the vehicle.” Of course! That high voltage can do damage to the vehicle in a number of ways.
This “ampere based system” is exactly what we have in fixed rate, non-automatic chargers.
Amps, at the charger’s rated value will be forced through the battery in any and all conditions. If the battery is in good condition, but recently discharged, it will absorb all these amperes efficiently. If the battery is fully charged, the cells will boil violently as the amperage is dissipated in the process of disassociating the water.
If the battery is sulfated, (see section C” below) a small amount of the amperage will slowly break down the sulfate and increase the charge of the battery.
The balance of the amperage will do the same as described for a fully charged battery. It will be wasted in consuming the water in the cells and in damaging the plates. Therefore, it is wise to use a very small charger (one or two amps) to recover a sulfated battery or to top off the battery on a monthly basis.
(Para # V)
B) VOLTAGE BASED SYSTEMS
With the advent of the newfangled electrical consumers on cars, beginning in the late 1930s, the ampere based system became inadequate -- it provided no way to supply the widely varying demand. So, the voltage regulator for cars was perfected, and our problems were solved. Well, not quite! Although drivers hadn’t really understood what the ammeter was telling them, they had gotten used to seeing it showing a positive FLOW of current. The voltmerer only represents the electrical PRESSURE in the system.
An additional difference is that the ammeter showed the current flowing into or out of the BATTERY (except for the starter), while the voltmeter shows the voltage in the entire SYSTEM. In the bucket analogy, the regulator’s job is to keep the bucket just full - no matter what loads are taking water out.
Theoretically, when the battery is “down”, the regulator senses less pressure, and increases the flow until the pressure is back up to the pre-set value. And, also theoretically, the regulator senses when the battery is “full” and cuts back the flow to just maintain the loads. That’s right, the amperage flow into a charged (or sulfated) battery is ZERO.
To say it another way, under the voltage system, the generator/ alternator’s job is to supply a constant voltage to power the many loads and, incidentally, to recharge whatever had been used from the battery.
The regulator hasn’t a clue that the battery is down, it just senses another load and carries it. The load goes away when the battery voltage comes up. Typically, the battery is recharged in a matter of seconds, and, while driving, the alternator merely supplies the devices required to make the car run, such as ignition, fuel pump, brake pump, etc., plus whatever loads the driver has selected.
This “voltage based system” is exactly what we have in a “tapering charge” charger.
Typically, these chargers will have an ammeter on the front, and they will supply a decreasing amperage to the battery as the battery becomes charged and it’s voltage rises. This type charger can be hazardous to a battery with a relatively low “normal” voltage.
For example, I have a 6 amp charger that, when pitted against my “best” battery:
(the one that hits 15.99 volts on the little one-amp charger) shuts down to well under a 1/2 amp value.
But, when placed on one of my “weaker” (deep cycle) batteries, it never falls below a full two amps. I can assure you that two amps into a fully charged battery is enough to create a violent boiling in the cells: and that’s bad.
A recent development is the fully automatic charger. The charger sends it’s rated amp value to the battery until the voltage rises to a pre-set voltage (about 14).
Then the charger shuts off and waits for the battery voltage to drift down to another (lower) value, at which time it turns on again. If the battery is in good condition, just recently discharged, it will absorb all these amperes for some time. Then, the on/off cycle will begin. As the battery is charged, the “on” periods become shorter and the “off” periods become longer. The “on” cycle is extremely short, so, although it is theoretically possible to recharge a sulfated battery, it could take weeks.
C) BATTERY SULFATION, CAUSES AND RESULTS
The invention of the voltage-based system was rather wonderful, and it solved a lot of problems. Unfortunately, it isn’t all wonderful. The reason that a battery will store, then supply, electrical power is that the sulfuric acid in the electrolyte wants to combine with the lead plates.As it does so, the compound LESD SULFATE is produced in the plates.
This chemical reaction is easily reversed by charging, if and only if, it is done relatively soon. If the lead sulfate is allowed to age, it hardens and becomes difficult to remove. The terms “won’t take a charge” and “sulfated” mean that the battery contains too much hardened lead sulfate to be usable.
These days, this is the usual reason for battery failure. Bottom Line: every lead-acid battery is in danger of falling prey to sulfation - BUT ONLY IF IT REMAINS IN A VOLTAGE BASED SYSTEM ALL THE TIME. Neglect the monthly service described in Section V. AT YOUR PERIL.
But, why does that alternator/voltage regulator team allow sulfation to happen?
The unhappy (for us) answer has two parts. First, “sulfate” has a very high electrical resistance, and, second, high battery voltage and high resistance both produce the same result - no current flow into the battery.
To illustrate, lets look at two situations. Case #1 -- Here’s the normal sequence for a good (not sulfated) battery in a car that had it’s headlights left on for a couple of hours. That’s about 20 amps X two hours, or 40 ampere-hours. Our battery is rated at 80 ampere hours, so it is about 1/2 discharged.
Pretend that we have installed an ammeter in the car in addition to the voltmeter. What will it show when we start the car?
When we turn on the key, the voltage will be lower than usual, and, when we hit the starter, the voltage will be “well below” normal. When the engine starts, the ammeter will register a LARGE value - probably more than 50 amps. In any case, it’s all the alternator is capable of producing.
Why? Because the voltage regulator senses that system voltage is low, so it increases the amperage in order to drive the voltage back up: thereby charging the battery.At first it takes a lot of amperage to bring the battery voltage up. But, as the battery charge rises, so does the voltage and the regulator cuts back on alternator output.
The ammeter will show that less and less amperage is flowing into the battery. The chances are pretty high that this engine will be shut off before the battery is fully charged allowing a bit of sulfate to harden.
If you had driven for a couple of days continuously, the ammeter would finally arrive at zero as the battery was fully charged.
Caution: If this should happen to you, ALWAYS use a charger to restore the battery to full charge.
Case #2 -- Lets substitute a neglected, 1/4 charged, badly sulfated battery for the good one we just described. We have to leave out the “headlights-left-on” part because this battery would have been stone dead in well under two hours.
As in the illustration above, the voltage is low. BUT, when we start the car, the alternator tries to push amperage through the battery, it meets a very high RESISTANCE, and the voltage goes right up to the “set point” of the voltage regulator, resulting in zero amperage flow.
Under these (normal) conditions, this battery will not improve, but will continue to drift downward over time, and will ultimately leave you stranded.
D) HOW DOES A BATTERY IN A FREQUENTLY USED CAR GET SULFATED?How/why does the battery in my frequently used Jag get sulfated, and what can I do to prevent it?
The answer is that you have a constant small drain on the battery that MAY not be fully charged back when you drive.
For example, in addition to the loss of charge due to internal chemical action (which is higher in warmer temperatures) the interior light stays on a while after you close the door, the radio security light flashes, the engine management computer is not totally asleep, and neither is the driving computer’s memory. Niggle, niggle, niggle!
If you look in your owner’s packet, you will find a large card which states: “CAUTION: To prevent a dead battery disconnect prior to leaving the vehicle parked for extended periods* (*2 to 3 weeks, depending on the state of charge at the time the vehicle is left)” That’s a pretty short time, and they’re talking DEAD battery! I’m talking SULFATED battery
So, gradually, over time, the battery becomes more and more sulfated.
Lets go back to the bucket analogy. If I ask you how much water is in that 5 gallon bucket, and you see that it is full, you will say: “Five gallons!”
You may well be wrong. There could be 4 gallons worth of rocks in the bucket that you cannot see. The water is at the rim, (the pressure is up) so the regulator thinks that the bucket is full. Get the point?
A sulfated battery is like a bucket with rocks under the water - it looks OK, but it is not full. You cannot get five gallons of water out of that five gallon bucket. If we add the provision that those rocks can be slowly dissolved, thereby restoring the bucket’s capacity, by slowly overflowing (overcharging the battery) we have the answer to the question: “How can I prevent sulfation ?”
You can’t! But, you can get rid of it before it becomes a problem.
A couple of sulfation stories.
1) When I bought my ‘92 Jag in ‘95, the battery was under a year old, but tested less than 1/4 charged, and was badly sulfated.
After a week on my one-amp charger, it was not responding so I got a new battery.
That old one went dead in less than a month just sitting on the shelf. Now, 48 months later, that “new” battery is still as strong as ever, but it will be replaced at 50 months: the end of the warranty period.
2) In 1994, my Father-in-law and I shopped for and found him an extremely nice 1989 Ford. I kept it in my garage for a time where I changed the tranny fluid and fixed several small things. Although the battery was badly sulfated, two weeks on the one-amp charger brought it up.But, some 3 months later, the battery failed while he was ten miles from home and in the rain.
Yes, he had a hard time locating a new one, and it cost more than twice as much as it should have.
Jaguar says it three ways:
First, “The service life of the battery is also dependent on its condition of charge.”
Second, “It must always be sufficiently charged for the battery to last an optimum length of time.”
Third, Therefore, we recommend that the battery charge is checked frequently if the vehicle is used mostly for short distance trips, or if it is not used for long periods of time.”
And I say: “RIGHT ON!”
E) WHY A SMALL CHARGER?Because our intent is just to “top-off” the battery, not to damage it. If the battery were to be truly discharged as in the “lights-left-on” scene above, a larger charger is fine. But all we need to do in our monthly servicing is force a small current through the month’s worth of sulfation in order to slowly dissolve it.
Any more than that will only boil the electrolyte, sluff lead off the plates, and shorten the life of the battery. Leaving a higher output charger on the battery after it is fully charged is bad for the battery.
Third section ---
XI. GREAT TRUTHS
A) GENERAL INFORMATION ABOUT BATTERIESa) All brands of batteries are not alike in their characteristics. They vary by voltage, by ease of charge, by resistance to sulfation, by length of life, by capacity, etc.
b) Batteries can fail due to internal defects, but do so only rarely.
c) Properly cared for, every battery without said defects, CAN provide excellent service well beyond it’s guaranteed life, but that is truly “borrowing time,” - not recommended.
d) There is never a “good” time for a battery to fail.
e) The modern battery/alternator setup is well engineered. Keep it at “spec” and it will serve you well
f) Batteries and electrical systems as a whole are not well understood by either mechanics or owners.
B) TECHNICAL INFORMATION ABOUT BATTERIESg) Over time, a hard deposit builds up between the battery posts and the connectors. Unless periodically removed, it will eventually block current flow.
h) Voltage regulators reduce the alternator voltage as the temperature rises in order to match the natural characteristic of the battery. The drop is about .5 volt per 40 degrees.
i) In reading a hydrometer, the specific gravity of the electrolyte must be adjusted for temperature as follows: for each 10 degrees above 80F, add 4. For every 10 degrees below, subtract 4.
(Example - at 30F, if the hydrometer reads 1.260, the actual value is 1.240)
j) Non deep cycle (car) batteries are damaged by being run down. (lights left on)
k) Approximate Specific Gravity for a full charge is 1.270, for 3/4 charge it is 1.240, for half charge it is 1.210, for 1/4 charge it is 1.180 and for discharged it is below 1.150.
l) Approximate off charge voltage at a fully charged battery is about 12.8, for 3/4 charge it is 12.6, for half charge it is 12.4, for 1/4 charge it is 12.2 and for discharged it is 12.0.
m) Battery power is reduced by cold temperatures. Compared to 80 degrees, at 32 degrees, the battery will have lost 45%: at zero, it has lost 60 %. (And at 32 degrees, the engine requires 65% more, and at zero it requires 150% more)
n) Battery electrolyte freezing temperature varies directly with the state of charge. At 100% charged it freezes at -70, while at 25% charge the number is 3 degrees. But, remember that any water added will freeze at 32 degrees until it has mixed thoroughly
o) A sulfated battery and a discharged battery may be two entirely different things.
C) ADVICE ABOUT BATTERIES
p) The cost of a battery is pocket change compared to the cost of a failure at the wrong time. Batteries are cheaper now than at any time in the history of the automobile - well under a dollar per guaranteed month.q) A new battery should always be slow-charged until it tests 100% full charge.
r) A battery that is discharged by accident (such as leaving the lights on) should be brought back to full charge with a battery charger.
DO NOT ask the alternator do it.
s) The difference in voltage between a fully charged battery and a fully discharged one is less than one volt. Therefore, only use a sensitive digital voltmeter to check voltage.
t) Always buy the BEST (big capacity and long guarantee) battery that will fit the car.
u) Given the choice, always buy a non-sealed battery. (Because you cannot test the electrolyte on a sealed battery)
v) Any water added to a battery cell should be distilled, de-ionized or rain water collected with non-metallic equipment.
DEAD BATTERY, BUT NOTHING WRONG! (From the January 1995 SUBURBAN INSIDER - a newsletter written by Ron Miller)
During that “Mother of all snow storms” back in December of 1990, quite a few cars stalled in traffic because their batteries went dead. Ever wonder how a battery can go dead while the car is being driven?Shouldn’t the alternator not only carry the electrical load, but recharge the battery as well?
The answer is “Yes, but.”
“But” the alternator must be “sound,” and it must be turned fast enough to carry the load. During that storm, drivers created a condition that we rarely see - prolonged idling with an unusually heavy electrical load.
Think about it! You are stopped in traffic, the engine is idling, the transmission is in “drive” your lights, heater fan and radio are on. Guess what? Unless your engine idle setting is on the high side, your alternator is producing less power than you are using, and you are discharging your battery.
Do it over a prolonged period, add a less-than-perfect (sulfated) battery, and she goes belly-up.
OK, so how to make sure it does not happen to you, and, how will you know it is happening?
Well, when you first get into your truck in the morning, turn the key to “On.” (Don’t start the engine and be sure the lights, fan, radio, etc., are off). Look at the reading on the voltmeter gauge. That is your “no load” battery voltage. Any time the engine is running, the voltmeter MUST show a higher reading than that, or the battery is being discharged, and you are heading for a breakdown.
So, if you find yourself in the situation described above, you can do one of two things.
First, you can raise the output of the alternator by increasing the engine speed slightly - usually just putting the transmission in “N” is enough.
Second, you can reduce the load on the alternator by switching to parking lights or a lower heater fan setting - but get that voltmeter up.
There are two mechanical problems that can only make things worse.
First, the alternator drive pulley is small, and, when under load, the alternator requires several horsepower to drive it.
Therefore, alternator drive belt tension must be just right, or it will slip, and that’s a sure fire recipe for trouble. (The new flat belts work better.)
Second, it is possible that the failure of a diode in the alternator will cut it’s output in half. You’ll never know it if you drive only in the daytime, but you won’t get far at night.
To test for these two problems, with the engine idling, turn the headlights on high beam, and set the heater fan to high speed. Watch that voltmeter. If the alternator is good and the belt is tight, the voltage will stay up in it’s normal range.
MY BATTERY CHARACTERISTICS - January, 1998 (examples only)
* ** Battery ___ Spec Grav (adj) Volts (@.5 amp) Volts (no)__Auto Time
JAGUAR 1.270 15.38 12.71 14S
BIG BLUE 1.270 15.32 12.79 12S
DELCO Sealed 15.99 12.91 14S
WV VAN (NEW) 1.289 15.46 12.85 16S
BATTERY “A” 1.280 14.02 12.72 9S
BATTERY “B” 1.280 14.03 12.65 7S
* - Voltage for full charge NOT on the charger
** - Time in seconds between charging flashes on the automatic charger Note: Batteries “A and “B are deep-cycle batteries
(C) 2000 Richard Miller