[T3] Battery

Jim Adney jadney at vwtype3.org
Fri Apr 12 19:41:21 PDT 2019

On 12 Apr 2019 at 23:49, J. Jonik wrote:

> Is there a way to check to find what, if anything, in a '71 Sqbk, might drain the battery in five or six days?    It was fully charged about a week ago...went for a nice drive with prospective buyer, but now, after sitting parked for most of a week, there's no cranking or anything.  Dashboard lights work.
> Or is this just the battery's fault...easy to find out, I think, at local Auto Parts store?
> But, just curious to know if something in the car could be draining the battery...and if there's a way to test to eliminate that question.

There are 3 questions that you need to answer here. The first is, 
"Was the battery actually fully charged when I shut the car down?" 
The second is, "Was there something draining the battery while it was 
parked?" And the third is, "Is this battery any good?"

It's easy to assume that the first answer must be yes, but that's not 
necessarily true. To answer that, you need to check your charging 
system, to make SURE that it's working correctly. The fact that the 
generator light went out when the engine started does not guarantee 
that the system is working.

To check the charging system, you need a voltmeter and know how to 
use it. The system voltage needs to be up around 14 V whenever the 
engine is running at medium RPM or higher. At lower RPM the system 
voltage can sag as low as the mid 12s. If you never see the system 
voltage rise much above 13 V, something's wrong with the charging 
system. If it doesn't get above 14 V the battery won't ever get fully 
charged. The voltage must be above 13.5 V for the FI to operate 

To check for a drain while parked, you can leave the car parked with 
the battery ground strap disconnected. If the battery then stays 
charged, you may assume that disconnecting the ground strap 
eliminated some leakage current.

Of course there's always the possibility that the battery is shot. If 
it seems to need a recharge after sitting unused for months, put it 
on a trickle charger for a week. In that time, it's voltage should 
slowly rise. Do NOT try to speed up this process by charging it at a 
higher current; that will damage the battery. If the battery voltage 
drops below 12 V after it's allowed to sit, disconnected, for a few 
days, it has a shorted cell and it's shot.   

Lots of FLAPS have the ability to test batteries to see if they are 
in decent condition, or at least if they are in a good charge state. 
I'm often skeptical about these tests, as they tend to be designed to 
sell batteries rather than actually tell you where the actual problem 

I have a charging system faq that I'll send you. If you're able to 
follow those more detailed instructions, that will allow you to check 
out your charging system and determine if it's working correctly.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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