Alternator or Battery?

Alternator or Battery?

Postby pops on Fri May 10, 2019 10:15 am

So I'm having an issue with my battery not holding charge which seems to be getting progressively worse, to the point where it is now discharging below the required voltage to turn the engine over if left for a day or 2.
The battery is 3 years old and is of high quality (supercharge gold) and when placed on a 7 stage charger does not indicate any faults so I'm starting to think I may have a faulty diode in my alternator.
Using my obd reader and torque app I can see that the alternator is charging ok at between 13.8 and 14V while the car is running.
Anyone had a similar issue or know how I might be able to diagnose the culprit?
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Re: Alternator or Battery?

Postby WUNSIE on Fri May 10, 2019 10:21 am

The obd reader might be indicating 13.8-14v, but what is it showing at the battery terminals, maybe give them a good clean and don't forget to check and clean the earth cable fixing point on Body/ engine
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Re: Alternator or Battery?

Postby MrCozy on Fri May 10, 2019 10:39 am

Had problem, not unsimilar to yours, but found my battery wasnt charging, but alternator was charging full output. Found that, at the positive connection to battery, where the fuselinks are, had melted plastic between the connections, and the other connection was loose as well. Had 16V at alternator positive terminal at fuselink, but slowly draining voltage at actual battery positive terminal. Should be reading 13.8V to 15V roughly at this point. Check and clean all connections, and retighten. Battery has inspection light? If so, and green, battery is fine. Black..dead cell in battery, time for a new one soon.
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Re: Alternator or Battery?

Postby pops on Fri May 10, 2019 11:58 am

MrCozy wrote: Battery has inspection light? If so, and green, battery is fine. Black..dead cell in battery, time for a new one soon.


Yep, Battery indicator is green but am not sure if that alone can be used as a reliable indicator
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Re: Alternator or Battery?

Postby explorer.dave on Fri May 10, 2019 12:23 pm

pops wrote:
MrCozy wrote: Battery has inspection light? If so, and green, battery is fine. Black..dead cell in battery, time for a new one soon.


Yep, Battery indicator is green but am not sure if that alone can be used as a reliable indicator


Just take it to an auto electrician, they can load test the battery and confirm.
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Re: Alternator or Battery?

Postby pops on Fri May 10, 2019 8:19 pm

Got to the bottom of it.
Took to an auto electrician who tested the battery, no problem there and he also confirmed the 14V charge at the battery terminals so alternator was fine but there was 400mA being drained from the battery with the engine off.
Got the multimeter out at home and found the head unit was the issue. Put the stock one back in and current draw was gone.
Best case scenario really, the bluetooth had been playing up on it anyway. Time for a new head unit :D
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