Maintaining battery charge - The Unofficial BMW M5 Messageboard (m5board.com)

dwasifar · 8th January 2002, 02:51

My work and travel schedule is such that I sometimes don't get to drive the beast for two or three weeks at a time. The last couple of times I've come home from a trip, I've had to jump-start the car (and it does NOT like it). Last weekend I got in on Friday night and had to jump it; it started fine a couple of times after that but in the morning it needed a jump again. The local dealer offered to do a load test on it and see if there was a draw somewhere; couldn't get me in this last weekend though. He also told me that the battery is not covered under the warranty? Is this true?

Anyway... for the moment I'm going on the premise that the battery slowly died during a recent month-plus idle period, and since then has never had a chance to fully charge. It's strong enough to start the car when it's warm but not when it's cold. So I bought a device called a Battery Tender, which is sort of an intelligent trickle-charger. It's intended to be left connected indefinitely; it will trickle-charge at 1.25A until the battery is fully up, and then go into an electonically-monitored "float" mode to maintain the charge. I hooked it up on Saturday. By Sunday the green light came on indicating the battery was fully charged, and the car started right up. Encouraged by this, I left it connected for the next storage period. I won't be driving the car again for a couple of weeks, probably; when I next try to start it, I'll know if it worked. I hope it does. But if it doesn't - does anyone have a good source for this battery besides BMW?

Wilkie · 8th January 2002, 23:39

I use Battery Tenders for all my cars that I don't drive regularly-- it's a great device and seems to work as advertised.

Although a battery is never the same after it has been fully discharged, yours is fairly new, so it still shouldn't discharge that quickly.

No, I don't know of a non-dealer source for a new battery, if you need one. The statement by your dealer that the battery isn't covered by waranty doesn't sound right. First of all, at least in my 7 series, the battery is a BMW battery, complete with the roundel logo. Secondly, if it is a non-BMW part, the battery (like the tires) should be separately covered by the manufacturer's warranty. If your dealer is worth anything, he should help you with that.

Wilkie

M5xtc · 8th January 2002, 23:48

Dwasifar,

I had the battery in my Chrysler T&C go bad while on a trip and the dealership I took it to replaced it...no questions asked, no pro rata, etc.

IMO, if the car is still under warranty the battery is covered

PhilSeastrand · 9th January 2002, 02:51

Your OEM battery should easily last 2-3 weeks without recharging. If not, the battery is bad and should be replaced, under warranty.

greg · 9th January 2002, 05:00

I have had my car sit for as long as 3 weeks with (knock wood) no problems. (My car will be 3 years old in february!!!) But batteries do weaken over time, and lead-acid batteries really don't like to get discharged - or even close. The more this happens the less likely they are to ever perform well again. They last longest when ALWAYS kept at or near full charge. So a proper charger (like the Battery Tender you describe) is a very good idea. (Older, and cheaper chargers that continuously charge are BAD - they WILL overcharge your battery, which causes it to lose water through evaporation, which in turn increases the strength of the acid to a point where damage to the lead occurs. )

Where did you get yours? how much? I'm thinking of getting one to stave off trouble BEFORE it happens....

AndyP · 9th January 2002, 05:18

My battery went bad about three months after I got my M5 ... once after I left my valentine on overnight and again when I used the aux ventilation. BMW replaced it under warranty but the dealership claimed that my valentine and my cell phone charger were way above the BMW recommended drain ... I ignored them and two years later the battery has never let me down and my cell phone and Valentine One are doing well.

Andy

Need4Spd · 9th January 2002, 06:38

Be advised never to replace your BMW battery with anything other than a genuine BMW battery. The BMW battery voltage is precisely tuned to trigger the alternator charging cycle. Aftermarket batteries tend to have higher average voltages, enough so that they fool the alternator into thinking the battery is charged when it is not. Over time, the battery will die as the result of not getting enough charge. When I read this in Bimmer Magazine some years ago, I thought it was BS until I was forced to use a very good aftermarket battery in my M3. Went thru 3 of them until I read the article and put in a BMW battery, and had no problems thereafter. You pays your money and takes your choice....

Jacob Lee · 9th January 2002, 07:56

Greg,

You can buy an intelligent trickle charger at Allison BMW. It even had a BMW logo on it - I was just there today and I wasn't even looking for one but saw it in the display window at the parts counter.

So after reading this thread, I figure I ought to go back and buy one and just have it handy when I go on vacation or something.

steveB · 9th January 2002, 15:50

dwasifar, i have had the same problem after not driving my car for 5-7 days. i tried to start my car yesterday morning after sitting for 6 days in my garage because of snow and it wouldn't start.

i have previously had my batter and alternator replaced under warranty. not a good sign that you have to jump a car that has been sitting for only 6-7 days.

DrRob · 9th January 2002, 16:28

As the Z8 has until recently been plagued with a battery-draining demon somewhere in the interactive phone compenastor harness (a fix is now available and came with mine), my dealer automatically provided a trickle charger at delivery.

It's called Advanced Battery Charging System from BMW, part # 82 11 0 026 663. It charges at a low rate of 1.25 Amps, having a microchip which maintains the battery at the precise float voltage charge which virtually eliminates battery destroying sulfation, a problem with many lesser performing battery chargers. It plugs into the lighter and can be left on indefinitely.

I don't know the cost as it was per gratis.

dwasifar · 9th January 2002, 17:33

Dr. Rob - except for the cigarette lighter connection, that device sounds exactly like the Battery Tender. 1.25A charge, microchip controlled, float-charge maintenance.

Greg - I got the Battery Tender at Pep Boys for $60.

For those of you who saw BMW's product, did it look anything like either of these?

Wilkie · 9th January 2002, 19:14

There are several manufacturers of these "smart" battery maintainers, in addition to the most popular, the Battery Tender by Deltrans. They are all reviewed in the current issue of Rider magazine.