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Float it! (archive)
[ Follow Ups ] [ 7-series (E32) Message Board ] [ Msg. Board FAQ ]
Posted by Kevin on June 03, 2001 at 21:31:04:

In Reply to: Battery Tender for 705iL posted by Scott on June 03, 2001 at 12:16:51:

Once you determine that the battery is OK (I agree, the dealer should verify the status and replace if any questions exist) You can use any charger that will put about 100 mA on the battery to 'float' it while the car is not in use. You can even put the charge into the system through the cigarette lighter (or other 12v access point that is not controlled by the key).

If you have an aptitude for electronics, there are a number of very simple circuits that you could use to accomplish this. Using a power cube (wall plug in transformer) that puts out ~ 16 - 18VDC @ 100 - 300mA, you can use an LM317T regulator with one small resistor to build a constant current regulator that would work nicely. If you're interested, let me know and I'll post the circuit. Otherwise, you can purchase float chargers made for this purpose from a number of sources (I've even seen 'solar' float chargers, but I have a hard time believing they really work well).

Kevin


I purchased my battery 9 months ago from a BMW dealer for approx. $150 and this weekend it was dead. The car is driven very little, it's a 93 with 36,000 miles and most drives are shorter than 30 miles with a long trip maybe once a year (2,000 miles round trip). My questions are, is this typical for this battery? Does anyone recommend a different battery? The dealer recommends installing a battery tender for est. $120 that I can plug in when not driving the car and it will keep the battery charged. They do not recommend any other battery (suprise!). Has anyone had this charger installed? They said it would be in the trunk or engine bay. I've fully charged my battery now and am thinking of having the dealer install this charger this week. Any comments will be appreciated. Where was yours installed, approximate how much, could I purchase one myself and install? Anyone have a source for this type of charger? I use an exide for regular charging. Thanks.




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