A simplistic calculation based on a max 90A charging rate from the alternator shows you
would need at least 1 hour of driving time to re-charge from a discharged stated, based on a
rated 90-110 Ah reserve capacity on a Gr 41 battery. This assume a full 90A output, and
100% charge efficiency of the battery, neither of which are true in reality. To be safe, I would
double this time, or better yet, use a good charger.
My Westy is parked for 2-3 months over the winter, and I've used a small 4A charger to
maintain the battery every month or so, leaving it on for 12-24 hours each month. This has
worked well for me - the original battery lasted 10 years before I replaced it last year. (it still
would start, but I didn't trust it in cold weather.)

On 9 Mar 2008 at 14:19, mordo <helmut.blong@GMAIL.COM> wrote:

> Excellent question, Loren. I was asking this myself yesterday after my van
> had died and i was trying to restart it.
>
> The van had sat for two weeks without being started. Prior to that, I had
> run the battery down by leaving the radio on but had drive for about 1/2
> hour after jumpstarting. Apparently, it was not enough to call it a helathy
> charge.
>
>
>
>
> ---------- Forwarded message ----------
> From: Loren Busch <starwagen@gmail.com>
> Date: Sun, Mar 9, 2008 at 1:16 PM
> Subject: How Long Running to Charge the Battery After Starting?
> To: vanagon@gerry.vanagon.com
>
>
> Here is a question for the Vanagon electrical gurus out there.  I've always been
> of the understanding that the folk wisdom of "If the vehicle is going to be
> unused for a period of time start the vehicle and let it idle for a while to
> keep the battery charged" was a bad idea because it took more energy from the
> battery to start the engine than you got back with a 'few minutes of idle'. So
> the question is, just how much engine running (at idle) or how much running on
> the road does it take to replenish the energy used to start the Vanagon?  BTW,
> this assumes easy starting, a healthy engine/FI/electrical system.
>
>
>
> --
> mordo
> 1990 Carat

Shawn Wright
http://members.shaw.ca/vwdiesels
'88 Westy 1.6TD 5 speed
'85 Jetta Diesel 1.6NA