43 My battery is not charging well, I am only showing 12V when charging rather than 13.4V. What is wrong?
Description
This article is from the VW Technical FAQ, by with numerous contributions by Jan Vandenbrande others.
43 My battery is not charging well, I am only showing 12V when charging rather than 13.4V. What is wrong?
A: There are numerous causes for this. Most of the time the problem is fairly
trivial. Going from cheapest to most expensive, try the following:
See also charge light diagnosis below.
- Check the ground connections, possibly install a new ground from
alternator to battery rather than using the engine block/transmission as
conductor. Forget trying to find the bad connection with an Ohm meter: Say
your alt. puts out 50 Amps, you'll get a drop of 1 Volt for each .02 Ohm!!!
Most VOMeters are not accurate enough in this range.
So, those tiny little resistances that have build up over the years REALLY
add up.
Use a THICK (10 or less Gauge/"AWG"), multistrand wire.
- Check the alternator wiring harness. Same reason as above.
- Clean all related connectors (sand paper, file).
- SOLDER ALL crimped connectors
- Check for an unusual drain (unlikely but possible)
- Check/clean/replace the alternator brushes (easy, see wear limits in
Bentley).
- Check the battery water level (use distilled water)
NOTE: DO NOT ASSUME YOU HAVE A MAINTENANCE FREE BATTERY BECAUSE IT
DOES NOT HAVE LITTLE SCREW TOPS. MOST VW BATTERIES ARE NOT MAINTENANCE
FREE AND THE WATER LEVEL SHOULD BE CHECKED PERIODICALLY!
- Have the battery checked (it may be shorting out)
- Have the alternator checked (diodes and regulator may be bad). Alternator
replacement is by the way trivial. If the alternator is bad, upgrade to a
higher amp one, especially in older cars and if you have a powerful stereo
system or aux lights 90 amp replacements are the current "hot" ticket.
However, some of the upgrades require a different wiring harness.
ND for example sells these and calls them their "Massive Overkill"
wires.
EuroCar had a detailed procedure on this about 1 or 2 years ago.
NOTE: Many car parts places will check out your alternator for free
or a very low cost. Sears used to do it for free in the US if you had
a DieHard battery, now they charge some nominal amount.
- Replace battery connectors with better quality ones.
(From D.J. Stern: number 1 or number 2 gauge Whitaker brass-terminal
battery cables.)
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