charging battery

Brett Dikeman brett.dikeman at
Thu Jul 2 10:51:14 PDT 2009

On Mon, Jun 29, 2009 at 12:24 PM, robert
weinberg<centaurus3200 at> wrote:

> quick question. my battery is dead because i haven't driven the 200 fpr 3 weeks. once before, i set the charger to 2 amp trickle for 10 hours and it worked. this time,
> the battery is still dead. this is with the positive clamp on the positive terminal and the negative on the chassis as dictated by the battery charger instructions.

2 amps for 10 hours is less than 20AHr, and most car batteries are
~60.  That's *rated* capacity, which means "from 100% charge to 0%
charge", where 0% charge is considered 10.7V.  Anything below 10.7v
damages the battery.

Charge directly on the battery terminals, not via the splice, unless
it's an emergency.  The rear seat lifts with two screws which can
often be undone by hand or with a coin.

> i can up the ante to 10 amp, but the audi manual says to not exceed 6 amps. being i'd rather not fry my electrical system

6A is completely OK.  60?  No.  It's not the electrical system- it's
the battery.  Batteries have maximum recommended charge rates, usually
expressed as something like "C/4", which means for a 40AHr battery, it
is recommended to charge it no faster than @10A.

> i assume that means the 30 amp quick charge is out of the question, eh?

It is generally best to charge at the same rate of discharge.  Ie, if
the battery goes dead from self-discharge over the course of several
weeks, no, you shouldn't really put it on a 30A quick charge, no.

I strongly recommend an electronic, automatic, multi-stage charger.
The ones made by Vector are pretty good and widely available.

For long-term storage, a proper maintenance/float charger is required.
 Yuasa and Battery Tender, among others, make good maintenance
chargers; a couple of them are based off exactly the same OEM charger
board which has three lights spaced widely apart, red, yellow, green.
If you live in an area with strong sunlight, you can get a solar
panel, but it needs to be one of the large square ones, not the thin
5w-or-less units, which are next to useless.

What you do NOT want is a charger which switches on+off every so
often, which is what the cheap chargers do.  You want one that charges
the battery properly, then switches to a constant float voltage.

Lastly, make sure you check the battery fluid levels after it has been
sitting in storage, and obviously have the vent pipe properly
connected to prevent acid fumes from damaging the interior and
hydrogen buildup.


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