Kiwi01

I'm looking for some help in diagnosing a battery drain issue ... kind of long ...
symptoms: battery drains completely if I let it set for a few days
What I've done so far:
1) replaced old battery, original diagnosis pointed towards needing replacement ... 6 year old battery. Replaced with Interstate M91.
2) out of town for 10 days and the new battery was completely dead on return.
3) Charged battery ... checked voltage 12.77 across terminal without car running ... with car running 14.24 ... I assume the battery is good and the system is charging.
4) Two days later battery is dead again ... recharged battery again
5) next tested for a battery drain ... hooked DMM between terminal and ground DC amps is 0.104 A ... as i understand it 0.050 is acceptable. So I have something draining the battery.
6) next pulled each fuse individually with the DMM hooked up as before ... checked all fuses in "frunk" and engine compartment ... no drop from 0.095-0.111

Something is drawing from the battery. Taking a break for college football will leave battery fully charged but not connected and will check voltage tomorrow ... just to convince myself I do have some sort of "vampire"

Running out of Ideas ... any suggestions

1995 911 Coupe mostly stock, HID kit, after market amp that is currently disconnected, most other changes are suspension or shifting

Any help is much appreciated ... Gerry

Howdy993

Kiwi-

You might try putting a digital camera (video mode) in the trunk and closing the hood to see that the light is actually going out.

I recently switched the interior light from on when the door is opened to always off. Knock on wood, that has resolved my battery life issue.

Good luck

Beretta

Got the same problem some time ago.

Check the lights in the glovecompartment, front hood, engine hood is off, for sure, when you close them.

As Howdy says, I solved my problem with a mobilephone, put it in a videomode, put inside the hoods and glovecompartment.

Take the phone out, and watch the video to know is the lights go off.

For me, it was the front hood light that killed my batteries. Unplugged it, never use it, and my battery issue is gone.

Best of luck.

Kiwi01

Thanks ... I'll take a look ... I have already unplugged the front light but have not touched the engine compartment or glove box.

NC TRACKRAT

Unplugging the frunk light is just part of the equation. Check the microswitch below the frunk latch. Depressing the latch to the closed position should cause the microswitch to close, thereby sending a signal to shut everything down. If it's out of position or defective, the circuit can be left on, even though the light has been removed. You can hear the microswitch click when it closes. Use your DMM while holding the microswitch closed for at least 15 sec. It may show the elimination of the current draw.

IXLR8

The charging voltage is certainly good.

The 12.77V, was that after the charger was disconnected for at least 4 hours...preferably more? When charging your battery, you should take it up to 14.4V and maintain that for a few hours; charge current will drop off to near zero when that is reached.

Even at that you are draining 2.5 Ah per day, so after 2 days...5 Ah on a 50 or 70 Ah battery. If that battery was fully charged, you should be able to start the car after 2 days.

CCU fan on?

One thing to do would be to measure your battery voltage a day later, then two days later and post the results. Make sure your compartment latch is latched so that the luggage compartment light does not go on. I just can't see your battery voltage dropping that much on the drain that you have.

Howdy993

Agree.

My battery would take about 2 weeks to discharge to the point starting was questionable.

Has the battery been tested to see if all the cells are good?

Good Luck

Kiwi01

Again thanks .... I have another question then.

Past history was similar to Howard ... about two weeks for battery to drop enough to make starting tough.

Alex ... I may have thought the battery was fully charged because the voltage was reading 13.04 ... I didn't realize it should go up to 14.4 ... I let it sit for about 3 hours after it reached 13.04 and that was when it read 12.77.

So now I let the battery sit over night without being connected to the car ... the voltage dropped form 12.77 the day before to 12.64 the next morning.

Connected the battery again and let it sit for the day, 12 hours later voltage is now 12.57.

From what Alex said maybe this drain isn't that bad.

I am wondering if the problem is that I have not let the battery fully charge ... I have two chargers a CTEK 3300 and an older Sears 6amp charger. When I hook up the CTEK it shows green and flashes orange rapidly as long as it is connected. I haven't found any manual entry that covers those light combinations. It could be I was never getting a full charge on the battery. I disconnected the CTEK and I then used the old Sears charger and watched it closely. After the voltage reached 13.04 I disconnected it, maybe this was too soon.

My question then is it correct to let it the battery charge until I can get a a voltage reading of 14.4?

Thanks again in advance ... Gerry

IXLR8

The trouble with most cheaper chargers and the CTEK 3300 (I have 2) and Battery Tenders are, is that they usually go straight to a float mode when they reach 14.4V instead of remaining there for a few hours or until the current decreases to a certain low value (less than 1 amp).

The 13.04V that you see might be the charger in float mode, although that is about 0.5V low (battery type dependent). 13.5V is usually a float mode.

I bought a used lab grade HP lab grade power supply off ebay 10A - 40V, so that I can control off season charging.

12.64V might end up being your "rest" voltage, which is pretty normal for a plain old flooded lead acid (FLA) battery.

If the battery was left disconnected (you connected it again...not a test of a battery's charge holding ability), it should not drop to 12.57 overnight. General rule of thumb for a conventional FLA battery is 0.1V drop per month.

I would fully charge the battery and have it load tested. Capacity tests give the full picture, but take too long.


My CTEK never flashes its LEDs unless the unit is powered and disconneted from the battery. Check your connections to the battery. Polarity correct?

Take your other charger to 14.4V and let it sit there for a while. If it overcharges, I believe your 91 battery has filler caps for topping up if necessary.

Kiwi01

Thanks Alex ... I appreciate your knowledge, common sense and input. Some of you past posts have been very helpful in helping me to begin to understand batteries and chargers. I'll use the old charger and take it up to 14.4 V and go from there. I'll try to post the results.

... Gerry

IXLR8

Gerry, the reason why I asked you to check battery voltage day after day was to see if your battery retains a charged state. And for that test, the battery should be disconnected for the full length of time of the test and not connected to a drain at any time.

Once a battery has had its absorbtion charge (14.4V and current tapers off to near zero...a matter of time) and the charger is disconnected, battery voltage will drop quickly and over 4 to 8 hours will stabilize at its final voltage (12.60V to 12.9V depending on battery chemistry).

After that, self discharge (battery not connected) should be very low (max 0.1V per month or ~0.003V per day) unless you have an internal electrical drain within the battery higher than mentioned above.

Check the CTEK troubleshooting guide. They mention flashing LEDs. You may have a battery or connection issue.