View Full Version : Checking for discharge

12-06-2010, 04:05 PM
What is the best way to check for a draw/discharge of the battery? I had a battery FULLY drained by douche wreckers who turned my lights on and left them on for three+ days. I had to charge the battery off another vehicle and jump start it to get it home, but then it would not start the next time I tried (after a couple days) so I attempted to charge it with my battery charger. When I initially tried to recharge the battery my charger gave an error code for open cell or sulfated condition. I ran a short "desulfate/recondition" cycle and after that the battery charged. Started the car and verified that the charging system is working (14.5 volts at the battery and output from the alt). Checked the battery again after it ran for a few minutes, solid 12.5 volts (with engine off). Car sat overnight and the next day at 11.5 volts and won't start. I took the battery into napa and they believe the car likely is draining the battery. I didn't get into the history of the battery with them nor did they ask for any information so it's really just a guess/assumption on their part, but, if they come back and tell me they don't want to replace the battery and I must have a draw/discharge in the car, how would I best check for that?

12-06-2010, 05:28 PM
Well, the easy way to check if you have a draw is to loosen [don't remove, just loosen] your negative battery terminal, get a test light, attach the clip to your negative battery terminal, touch the point of the test light to the top of the neg battery post and while keeping the test light touching lift the terminal off the post.
Light should not light up [car should be off, no key, doors closed and sat for a min or two].
If it lights up you have a parasitic draw.

To test how much of a draw you have, hook up a multimeter to the battery [same way as the test light, same conditions], set it to amps and remove the terminal.
You should have less than 50 mA. If it's an older car, way less. If you end up with like 55 or something it's fine too.

I would charge the battery til it's good, then drive the car for like 20 min or so.
Might give the battery a better charge.

12-06-2010, 09:21 PM
Napa claims the battery is just fine, so I'll pick it up and run through what you've listed. Thanks!

12-07-2010, 02:48 AM
I don't have a test light, but I did check it with the multi-meter. Unless I'm doing something wrong, I seem to be getting 20mA. Initially it idled for about 10 minutes with the radio, headlights and radiator fan running. Voltage never dropped under 14 volts both at battery and from alternator. I then drove it for about 10 minutes and when I got back read about 12.5 volts at both battery and from alt regardless of what accessories I turned on or off. I then shut the car off and still read 12.5 volts at battery, but also still 12.5 from the alt (is it normal to have voltage from the alt with the car off??). But then when I restarted the car only about 2 minutes later, I'm getting 13.9/14 volts again at battery and from alt, again, regardless of accessories being on or off. I'm not certain what this means, if anything, but I'll see how it is in the morning after sitting overnight.

12-07-2010, 04:30 AM
You're supposed to have battery voltage at the alt power wire with the car off, the power wire runs to the fuse box and then to the battery [that's how it's charged].

The alt will charge less when the battery is fully charged. If the battery is low [or you have high drain from accesories] the alt will raise it's output.
However, 12.5 sounds low, even if it's fully charged. It's possible a very weak/bad battery could damage the alt voltage regulator.
Keep an eye on your output power from the alt for a while, regardless of what battery is in there.

12-07-2010, 04:36 AM
gawd...saw the thread title and half expected something comepletely different in this thread...

I think my battery just gave up on me today as well...GRRRRRrrrrrr.

12-07-2010, 04:47 AM
gawd...saw the thread title and half expected something comepletely different in this thread...

*facedesk* I didn't even notice that.. but don't worry, that would only be in OT and posted by Ricksta... :hehe:

Alltracman - Alright, I'll be keeping an eye on it (carrying multimeter in the car) and see how it goes. It's worth noting I suppose that the alternator is a napa replacement unit and I've just had to repair the wire bundle that runs to the alternator (exhaust leak cooked them and they broke). I'm hoping that the repair was effective and this isn't still symptoms from that. I cut out the brittle lengths of the worst wires and soldered in new ones, shrink wrapped the connections, then taped and bundled it all in flexible sheathing.

12-07-2010, 10:44 PM
Well it seems pretty obvious it doesn't have parasitic draw at this point. Started fine in the morning, showing 12.5 volts at batt and alt. Drove 15 minutes to work after idling for 5 or so. Checked voltage there, 12.5. Drove it 5 minutes around lunch time, didn't check voltage. Drove it home a couple hours after that another 15 minutes... voltage at 13.9ish with parking lights, fan, radio and heater on. I don't quite get the numbers jumping around like that but if it doesn't drop lower than 12.5 I guess it's ok (I still think it's weird to be dipping down there so often, but eh). Maybe it's just a symptom of a crappy reman autoparts alternator.

12-07-2010, 10:50 PM
A Big 3 upgrade makes sure your charging system is in healthy order. Doesn't hurt to have the extra wiring.