Charging System?

[Robin Toor]

Becuase I failed aircare and used up my 3 month temp pass during the summer, I have to travel by temporary insurance passes, and since I get a ride to school, I havent driven the car in a while...

I charge the battery every month or so.... and it dies in about 3 weeks, with the alarm off and nothing else on.... I guess 3 weeks of the battery just sitting there 100% until it dies is average, so the battery looks good. Its an optimal series red cap battery....

so I go to start it up... and the battery is completely dead, I charge it on 12 amps, and within 2 seconds it says it is 100%.... it normally takes almost 6 hours to charge it.....

so I go to start it again, and sure enough, the battery is dead, but the charger keeps showing 100%! Finally I plug the charger in somewhere else and it charges fine. I let it do so for about an hour, and come back, and BARELY start up the car...

it idles at 750rpm or so normally.... then I rev it to 2000 rpm, it comes back down, then it stutters, idles at 500rpm... 200rpm.. then dies.... try to start it again, sure enough the battery is dead again

jump start the talon with the beemer, rev the beemer up to 2000 rpm for around 3 minutes to charge the talon, start up the talon, and it does the same thing again, idles fine, rev it to 2000rpm, then is just about to die... idling at 100rpm! then when I just think it is just about to die, the rpm's shoot back up the 750 and everything work fine..... what the hell is going on?

It might be the battery, but I think my alternator is gone and is not charging my battery at idle, so it keeps getting drained, and then finally the alternator kicked in and everything was fine......... any opinions? is it the alternator? Is 3 week battery life about right for an optima battery?

[Andrew Scott]

It sounds like your battery isn't charging it for sure. It should put off enough current to at least keep the car idling.

You might want to consider disconnecting your negative battery terminal if you leave the car longer than a week. My battery dies in about a week if I leave it sitting.

[Kevin Jones]

Here's my two cents.

Originally the battery probably died from being drained completly numerous times.

It's probabley idling weird because the computer has to relearn it's ways, which takes more than a few minutes.

I jump started my sister's truck with my Talon and wrecked my alternator. It's possible this happened to you while jump starting if you had the BMW running at the time.

[Robin Toor]

oh crap jump starting can ruin the alternator? I jump start or get jump started all the time...

how do you wreck the alternator by jump starting? I hope I didnt wreck the beamer's alternator.....

[Kimyee Lai]

Note, the alternator doesn't REALLY charge the battery until over 2000RPM anyway...which is why you need to go on a freeway cruise to charge up your battery.  Get your voltmeter out and measure the voltage.  (it might actually be a loggable item on DSMlink  If your alternator is dead, when you rev it up your voltage will stay around 12v.  

I think your could damage your alternator if the car being jump started starts revving before the cables are disconnected.  If the startee alternator produced a higher voltage than the starter alternator, you COULD blow a diode/winding.  Which is why they tell you to connect the negative of the starter car to an engine ground point in the startee, so your startee voltage would be lower than your starter alt voltage.  

You should also get a current meter, the one that clamps onto a cable, and measure how much drain is on your car when it's resting.  That might be why you're toasting batteries.  It might be easier just to get one of those top-up chargers that will keep the battery alive.

[Robin Toor]

my turbo timer measures volts... but its always around 13.5..... so maybe its hooked up wrong.... of course I didnt check it today while the car was fucking up, but usually when the battery is fine it says 13.5 - 13.7

If the startee alternator produced a higher voltage than the starter alternator, you COULD blow a diode/winding.

in which car? the starter or the startee?

I have a battery charger I use once a month when the car is parked to charge the battery, I just forgot to use it this month....

[Mike Schmid]

Ideally you want a float charger on the battery 24/7 to keep it topped up.  It's pretty hard on the battery to be fully discharged then recharged.  Additionally, it's pretty hard on the alternator to charge the battery up from being dead.  

Not that it matters but I always thought the reason for using an engine ground as the last jumper connection was to prevent creating a spark right over the battery.  Where potentially it could ignite hydrogen vapours, however unlikely with modern sealed maintenence free batteries.

[Graeme Shaw]

Not that it matters but I always thought the reason for using an engine ground as the last jumper connection was to prevent creating a spark right over the battery.  Where potentially it could ignite hydrogen vapours, however unlikely with modern sealed maintenence free batteries.

That's what I was taught.

[Kimyee Lai]

Not that it matters but I always thought the reason for using an engine ground as the last jumper connection was to prevent creating a spark right over the battery.  Where potentially it could ignite hydrogen vapours, however unlikely with modern sealed maintenence free batteries.

True...that might be a more valid point than mine .

[Zak Mach]

this problem just happened to me.. i havent started my car in 2 months & my battery was completly dead.. jumpstarted it would go on but when i idled & try starting again dead ...so i plugged the charger in, it said the battery was 100% full.. i called one of my friends up at vader he said i have an optima battery.. (same as urs robin but mine is yellow top..) he just told me to leave the charger on overnight.. so i did & in the moring i went to my car heard a boiling sound from my battery & unpluged the charger.. waited 2 mins & started it.. & it started .. no problems...still going strong now.. this was about 3 weeksago..

[Zak Mach]

oh make sure u unplug the battery from the car before u charge it.. + & -

[John Hartman]

if there is very low voltage the ECU is getting incorrect voltages.  These voltages are one of the variables that the ECU uses to determine injector pulse width.  So if the voltage is low or fluctuating its gonna run like crap.

[Robin Toor]

ahhh ic.... also I heard the optima gel series battery takes a VERY long time to charge, especially when only running at idle... so maybe thats why it died out so fast... it doesnt charge well at idle....

even though the charger said 100%... and I hooked it up to the beamer and reved it to 2000rpm to charge the talon battery... so it should of been charged?

oh well, I'll check out the alternator and see how it is....

[Chris Clark]

Ideally you want a float charger on the battery 24/7 to keep it topped up.  It's pretty hard on the battery to be fully discharged then recharged.  Additionally, it's pretty hard on the alternator to charge the battery up from being dead.

Very true. Id get the alt checked out to see if it is putting out proper amps. The battery is long gone by now.

[Robin Toor]

you think the red top optima battery is dead? Should I get a new one?