Unofficialbmw.com

[dg27]

My new job requires that I travel for a month at a time several times per year.

I have a brand-new BMW battery and a BMW charger that I've never even taken out of the box.

I planned to use the charger to maintain the battery while I'm gone but wonder: Are there any disadvantages or long-term dangers to simply disconnecting the battery?

I know I'd have to reprogram the clock and reenter the code on the head unit and I assume I'd have to fully charge the battery upon my return, but that's not a problem since I don't drive every day when I'm home.

I rent a private garage and I feel kind of funny asking the landlord to let me keep the charger plugged in the entire time I'm away.

I'm also not crazy about leaving the hood ajar the whole time.

Any advice would be greatly appreciated. Thanks.

dg
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1998 Morea Green 328is 5-speed sports pkg
~165700 miles

[PJK]

I see no problem in disconnecting the battery other than the bother of doing so and re-entering the radio code and setting the clock.

If the temp and humidity ore not extreme I would not expect to have to recharge the battery after one month.

If you leave the battery connected and do not use the float charger you will lose a good bit of the charge in one month.

Phil

[dg27]

Phil:

Thanks for your reply.

I'd really rather not use the charger, so this is good news.

Question though, re: this:

[PJK]

Hi dg,

I seem to remember measuring ~30 mA of leakage in my e36. Figuring 30 days in a month that works out to about 22 AH in one month. Now days they don't state the AH capacity of automotive starting batteries but I will quess 70 AH. After one month I would expect you car to start. I wouldn't do two months and three months is really pushing it.

Storage batteries have several hundres charge / discharge cycles before they are worn out. It is looking like one month with out disconnecting your battery or connecting the float charger is obout 1/3 of a cycle.
Id doesn't look like a huge deal but I would expect you would get longer battery life if you disconnected the battery or connected the float charger.
Of course if the charger is not properly calibrated it could depleat the electrolyte in the battery.

Phil

[dg27]

Update: Took my chances and used no charger and didn't disconnect the battery. It was fine when I got back.

dg
_________________
1998 Morea Green 328is 5-speed sports pkg
~165700 miles