battery keeps going flat,,

[92mr2paddy]

ok so got my supra back from tune etc and all running good, go for a quick drive then few days later battery dead, jump it, all ok, next few days same thing dead as,
so i unplugged battery after last drive and then few days later connected it back up, car starts fine,,
so i checked everything i could think of door lights, glovebox light etc etc, nothing is on when key is out, still battery ends up flat,, how do i check if current is being drawn off and what is using it,, btw battery is brand new also.

thanks pat

[jondee86]

Could be a faulty diode in the alternator.

Cheers... jondee86

[Grrrrrrr!]

Connect a multimeter up to measure current coming from battery, then pull fuses one by one till the current draw drops. Start with stereo gear and alarms and that sort of aftermarket stuff first, its the most likely, or whatever was played with recently.

[AE82 FXGT]

First basic check I'd do is make sure it's charging.
Check voltage with car off, should be around 12v
Check voltage with car running, should be 14v (ish can vary a bit depending on car from 13.8 to 14.4v)

After that check for current draw as said above.

[92mr2paddy]

yep will try the fuse thing, will have to hunt down a multi meter no biggy, im guessing after jumping car then disconecting battery after a drive and it then starting again later the alternator is doing its job? will check that also tho once got the meter. thanks

[B1NZ]

yep will try the fuse thing, will have to hunt down a multi meter no biggy, im guessing after jumping car then disconecting battery after a drive and it then starting again later the alternator is doing its job? will check that also tho once got the meter. thanks

It might not be charging to its full capacity so might be giving you enough to keep electrics running and the occaisional start but not charging the battery to its full capacity if that makes sense?

[AE82 FXGT]

Starting a car is the most stressful thing a battery does, cranking the starter/engine draws a lot more current than anything else in the car (excluding monster AV set ups).

[92mr2paddy]

yea but the battery will be flat as, not even the clock is on after a couple of days so whatever is draining it must be doing a good job, car has a simple headunit no stupid big sound setup or anything else, no alarm no turbo timer, will buy meter today and give it a quick check over tonight.

[Mr Ree]

JZA80 alternators often have issues, might be time for a spare...

[92mr2paddy]

so results after jumping again,

13.2ish volts when running , seems wayy to low, had car running for ages and turned of and battery only has 11.5volts, so will test tomorrow if the battery still has 11.5volts if not then there is current being drawn.

yea looks like i need a new alternator also, can they be rebuilt/serviced?

[whynot]

some of the fancy new batteries need higher voltage than the good old lead acid. is it possible that your new battery is a fully sealed calcium type and the alternator is just not up to charging it properly?

[Lloyd]

It may pay to get it checked properly. Get it actually charged rather than relying on the alternator and test things then.

13.2V at idle or with a few revs on? You may find it's lower at idle, which is normal on some cars. If the voltage is closer to 13.8ish upwards with some revs on then the alternator should be doing its thing.

Charge the battery and get it properly load tested. It may sit there saying 12.5V after a charge, but on a decent load test it could drop off to 8V (under load) and then read over 12V again sitting there doing nothing.

[matt dunn]

13.2 at the battery is not really enough for any battery,

check it at the alternator but symptoms sound like the alt is toast.

[allencr]

Yes, 13.2 is on the low side but still OK, you've already seen that the alt. is good enough to charge up a flat battery! Find the current leak first, the alt may last years.
No need for a meter, just a bulb between post & cable will tell if there's current being drawn, a small wattage bulb like a dash light will be barely red for the ECU & clock while a headlight wouldn't show at all. If the bulb's bright, disconnect stuff like the alt. & pull fuses till you find out what shuts off.

[92mr2paddy]

tested battery this morning and found the standing volts had dropped from 11.5 to 8.5volts. will jump car again and check if alternator is giving any more juice at higher revs as i'm running a ATI damper and they are 'slightly' smaller diameter but by f-all.

next step is to charge battery with trickle charger till full and disconnect battery competely and see if the battery holds charge over a few days as its brand new.

any other ideas guys? cheers

[92mr2paddy]

Yes, 13.2 is on the low side but still OK, you've already seen that the alt. is good enough to charge up a flat battery! Find the current leak first, the alt may last years.
No need for a meter, just a bulb between post & cable will tell if there's current being drawn, a small wattage bulb like a dash light will be barely red for the ECU & clock while a headlight wouldn't show at all. If the bulb's bright, disconnect stuff like the alt. & pull fuses till you find out what shuts off.

not too sure what you mean by post & cablce et,. how exactly would i test each electrical part etc? thanks

[allencr]

You want to find out when current is moving/being drawn, so connect an amp meter in series, disconnect the cable and using the gauge or multi-meter or simply a bulb to bridge the gap.
One lead to the battery, the other lead to the cable that was disconnected, with whatever you're using to sense the current draw is in between them.
Alt will have to be disconnected, either at the alt or battery terminal or whatever its got. Everything else should be at the fuse box/s.

[stoffa]

Is it a calcium battery? They need a special charger otherwise you'll get 3-4 starts and they run flat again. A calcium mode battery balance charges the cells evenly I believe.

[92mr2paddy]

not sure if calcium battery i think its just normal acid type, its a ultra battery (white one)

anyway i jumped battery to get some volts back into it as only had 3volts left.
car i was using was putting in 14.4v so atleast thats got a good alt. started going through the fuses and found one drawing small amount of current.

so ive left it charging a bit and battery is at 12v, took fuse out and have left it out and will check tonight if voltage is still dropping, funny enough according to the fuse box its the alternator fuse,, is it possible that a faulty alternator could also be drawing current when car is off???

[Grrrrrrr!]

Meter set to 2000uA, reading 119 so 0.000119 Amps? Thats not the problem. Keep looking.