I need to replace the battery in my E46 M3 'vert. Rather than making a trip to buy a battery and a return trip to bring back the old one, I'd like to do it in one trip in my daily-driver. That would mean the battery would be disconnected for 1-2 hours minimum. Can I hook up my Battery Tender to the under-hood connections to keep the car "powered" during this time? Do I even need to? My concern is leaving the car with no battery at all for hours would cause loss of settings/memory or some other detrimental effects. Normally a battery swap would only take a few minutes.
I have had success doing this on my '01 E38 with my BMW battery tender/trickle charger, but find that folks are generally apprehensive to recommend things like this. Out of curiosity, what settings/memory are you worried about losing? As soon as the new battery is in, seat memory is as easy as pressing "M", "#" (which at least gets you back 1 of the 3 possible memory settings). Radio stations will take you 30 seconds to setup again. Clock...another 10 seconds. Can't think of anything "detrimental" at all though...... Cheers, Tim ps: I replaced my battery yesterday which is why I'm asking
my 04 325xi kept it's radio presets when I disconnected my battery, only thing I really lost was the clock
Seat, clock and radio I'm not so much worried about. Heck, I don't even use the radio. I was concerned there might be "hidden" effects of having the battery disconnected for more than a couple hours, such as the whole darn car not working when I put the new one in later. Normally I wouldn't worry about such things, but this is a BMW and quirky stuff like that (things that require dealer maintenance) wouldn't surprise me!
I've seen the dealer hook up one of those portable jump start devices when changing the battery or some other electronics. It is typically only left on for a 1/2 hour or so, best I can tell.
Take a ratchet with a 10mm socket and you can change it where you buy it. My battery went stone dead for several weeks while in storage on my e46 vert with no adverse impact on the systems.
Update: When I changed my battery a few weeks ago (about the time I stumbled onto this post), I left my car with no battery for 3 days until I got a chance to install the new one. Not a single setting was lost. Personally, I wouldn't bother messing with the battery tender IMHO. Hope that helps, Tim
No probs... I've DIY disconnected the battery several times on my old 750iL and my 540iA with absolutely no ill effects so your concerns are unwarranted. You can feel totally safe disconnecting the battery without suffering any major issues. The only minor losses have been mentioned above so swap away!!! You can also follow the other suggestion, which was to replace it in the parking lot. Another possibility would be to purchase a "memory tender" that has a 9-volt battery that plugs into your cigarette lighter socket and maintains all the memory settings so you won't have to reset everything later...best of luck!
