Charging C4 Battery using jumper positions

[Mark Rosenkrantz]

I think all Motronic and newer ECUs have batt+ lines, from memory.   How it
switches internally, I don't know.

Mark Rosenkrantz

On Tue, Aug 2, 2011 at 10:06 PM, Cody Forbes <cody at 5000tq.com> wrote:

> Technically if, while charging at 30-40 amps, your battery voltage exceeds
> 15.5 volts then you have a battery with sulfated plates that needs to be
> replaced. Your ECU should be able to handle that much voltage during that
> period. I've seen voltage at 16v for short periods of time when I had to
> nurse one of my cars home with a bad voltage regulator, it would spike high
> and I'd add some loads (lights, defroster etc) to draw it low then after a
> few minutes it would start going low so I had to turn the loads off etc. ECU
> still functions properly a year later.
>
> Thinking about that a bit more your ECU shouldn't see any voltage anyways.
> IIRC With the ignition switched off the ECU on a C4 is not connected to any
> power sources (C4/urS guy please confirm). I know to be a fact on the older
> Hitachi ECU equipped cars, but the Bosch ECU *might* have a constant power
> line.
>
> -Cody (mobile)
>
> On Aug 2, 2011, at 9:53 PM, Jay M <jaybird002 at msn.com> wrote:
>
> >
> > Thanks Tony, Huw, Steve, Christopher, Mike, Eric & Mark for your
> responses. I guess I am a creature of habit with both new generation and old
> gen cars. That is to say, when I encountered the rare dead battery in one of
> my cars, and when I say "dead" I mean really drained to the point where
> there is absolutely no power left in the battery to illuminate even the
> smallest 1 watt dash light (which was the case today)..... I always removed
> the battery to charge it back up with a battery charger to at least 12.5V in
> order to save the alternator the work and strain of recharging the battery.
> In addition, I guess another reason for me and perhaps more importantly, was
> I have read horror stories on other forums regarding charging batteries in
> cars equipped with an ECU where the ECU was fried due to supposedly
> overcharging of the battery while the battery was connected. Subsequently, I
> was always hesitant to charge the battery while it was connected to the car
> for fear of overchargin
>  g
> > and consequently frying the ECU.
> >
> > Date: Tue, 2 Aug 2011 16:20:42 -0500
> > Subject: Re: Charging C4 Battery using jumper positions
> > From: auditony at gmail.com
> > To: jaybird002 at msn.com
> > CC: quattro at audifans.com
> >
> >
> >
> >
> > I was under the inpression VAG did that changeover in 2000, so I'm
> surprised it remembered the code.
> >
> > Yes, you can charge the car just as jumping it, from those posts. It's a
> direct link to the battery, so it will work just the same as hooking
> directly on the battery.
> >
> > Tony
> >
> >
> > On Tue, Aug 2, 2011 at 3:41 PM, Jay M <jaybird002 at msn.com> wrote:
> >
> >
> >
> > Hello everybody,
> >
> >
> >
> > Just curious, on our 1996 A6 my wife left the key in the ignition in the
> first on position overnight and needless to say the battery was totally dead
> this morning upon startup. I removed the battery from underneath the rear
> seat and used my trusty old Sears 6 amp battery charger for a 6 hour charge
> on the work bench. My question is in the future if I need to charge the
> battery using this battery charger can I just charge the battery using the
> emergency battery jump positions under the hood near passenger side
> firewall....that is to say the positive lead from charger to positive
> emergency jumper post (underneath black plastic cover) and negative lead
> from battery charger to good chassis ground up front?
> >
> >
> >
> > Also, I was surprised upon reinstalling battery that I did not have to
> input my radio code for the original Bose stereo. The radio turned on fine
> and did not display the usual CODE message telling me to input the radio
> code. All my other present and previous C4's are and have been 1995's so
> this is the first Audi C4 I had that did not require the code when the
> battery was disconnected and then reconnected. Is this normal for a 1996?
> Thanks.
> >
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