944Speedy944

I’ve been having incredible difficulty diagnosing and fixing this electrical issue I’ve come across,

For context my 944 has a brand new 90 a alternator and a brand new battery,

however as of recently the 944 while idle or driving will drain battery at a pace of about .03 v a second, which kills the car entirely in about 30 seconds give or take, for redundancy I’ve cleaned the grounds on the front left behind the headlight, tightened starter and alternator bolts ( just in case ) battery bolts are very tight too. And I’ve checked every fuse available in the upper and lower fuse bank.

Currently when on the electronics on position ( 1 ) the battery sits at 3.6 volts, when the key is out of the ignition the battery climbs and sits at 11.3 volts. At idle the car will start at 11 and fall down to around 6.3 before completely shutting off
when removing the relays I’ve found my f5tech dme relay increases the battery power to roughly 5.5 v

so far this is the only relay to show any results,
I am completely stumped as to what’s going on considering the battery actually stays at 11.3 ish when completely off but loses a whole 8 volts when the electronics come on

any help or tips, or even just redundant checks I can do would be greatly appreciated, sorry for the super long post just needed to clarify all my reading so far

( p.s if it counts, the alternator is a duralast from autozone, which means it could have just failed but that doesn’t explain some of the other things considered)

jeyjey

If your new alternator is junk, then it could have easily killed your new battery. The battery might be holding a surface charge, but with no current-capability behind it. Do you have access to a carbon pile battery tester to test it on? (A multimeter will only tell you the surface charge.)

T&T Racing

My suggestions are:
1. Disconnect the battery lead (+12v) at the alternator. To safely do this, first remove the positive terminal connector at the battery. Secure the positive lead at the alternator so it cannot ground. Measure the voltage at the battery terminals. If not close to 12.5 vdc, recharge the battery.
2. Reconnect positive battery lead. Measure voltage at battery. Should be 12.5 vdc at full charge.
3. If step 2 test fails, low voltage, then short in battery lead to alternator.
4. If step #2 is OK, then remove positive battery connection, reconnect alternator positive lead and reconnect positive battery terminal. Measure voltage at battery. If not 12.5 vdc or voltage is not steady but decaying, then there is a short to ground in the alternator.

944Speedy944

I do not have access to a carbon pipe battery tester, however I do have access too a secondary battery that is brand new for a different car, could it be a possibly that the battery just didn’t make it a whole 4 months or do you think maybe the alternator significantly shortened the lifespan, I think it could be the battery considering it will sit at 11 when not hooked up but can’t hold any voltage when powered

( p.s ruled out the fuses and relays for this issue )

orig944

Your alternator is not doing anything and your battery is flat, but potentially not bad. Take the alternator to an auto parts store and have them test it. Bring your battery as well.

944Speedy944

so, I didn’t see this, and I went and claimed the warenty on the battery since it wouldn’t hold a charge under load, I have a new “ upgraded “ battery so I will see how it goes, the battery now holds charge sits at 13.5 and will charge undsr a full load ( radiator heater lights fog ect ) and it still charges ) however it still could change cause this was how the old battery acted I will keep this forum updated if anything changes

jeyjey

> could it be a possibly that the battery just didn’t make it a whole 4 months

If the battery was stored for any significant portion of that time without a charge on it, then yes, the plates could have sulphated.

Anyway, run @T&T Racing 's checks with the new battery.

944Speedy944

will do thank you, to clarify though. The battery had not sat at any low charges for any period of time and the issue had been noticeable for a month or two prior to it almost completely failing. ( with the car almost dying once or twice beforehand but never as bad ) however, what seemed to make it worse was the battery being in the car outside in -10 degree weather over the span of almost 5 days. Doesn’t explain the prior incidents though

anyways thank you I will check it out

jeyjey

Battery output will be significantly lower when that cold, but that mainly impacts starting. It shouldn't cause the battery to go flat when running.

Tiger03447

When doing ANY kind of electrical work on any car, undo the NEGATIVE (ground) side first. Then undo the positive side , to remove the battery. When reconnecting the battery, put on the positive terminal first, then the negative. If you do this by doing the first advised method (IMHO), when you go to reconnect with the ground already connected, there’s a pretty good chance of frying the alternator diodes with the current surge. So, negative off first, and reconnect it last. This is also good info when using jumper cables.

CliveB

Tiger is quite correct in their advice to always disconnect the negative battery terminal first and connect it last but the explanation is incorrect.
In an electrical circuit (clue's in the name) it doesn't make any difference in current flow where you break the circuit.
The real reason for disconnecting the negative terminal first is that if you accidentally short your spanner to the car body or other earth it does not result in serious trouble.
By serious.I mean burns from massive cuttent flow, pain from smacking your arm/head when you jump backwards in response to the sparks or, by far the worst, the possibility that the battery could explode.

In context to the thread, it pays to remember that leaving these cars unused for more thatn a few days can result in the battery losing charge. Especially noticable when the days are cold and if journeys are short.
I disconnect my battery (negative first!) whenever I'm not expecting to use the car for more than a few days.