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-   -   Have I a duff battery (https://www.the75andztclub.co.uk/forum/showthread.php?t=315756)

macafee2 11th October 2021 08:43

Have I a duff battery
 
I took the battery off the car and put it on charge for a few days in the garage.
As soon as I took it off charge I measured the voltage and it was 12.8v, another battery that had been off charge for about a week measured 13.2v.

The above was about 3 or 4 days ago, I have just measured the suspected duff battery again and it is 12.57v. Not a lot of drop but as it was 12.8 when it came off charge I am suspecting it is duff.

Your thoughts please. If you too think it may be duff I will take it back and the shop can try a drop test.

macafee2

MSS 11th October 2021 10:20

I wouldn't say the voltage you have measured necessarily indicates a duff battery.

I would put a mild load on the battery for a while and recheck the voltage. An old 55W 12V headlamp bulb consumes nearly 5Amps and makes a good test load.

macafee2 11th October 2021 10:39

Quote:

Originally Posted by MSS (Post 2903178)
I wouldn't say the voltage you have measured necessarily indicates a duff battery.

I would put a mild load on the battery for a while and recheck the voltage. An old 55W 12V headlamp bulb consumes nearly 5Amps and makes a good test load.

At say 2 minutes, what would I expect to see voltage wise?

macafee2

MSS 11th October 2021 11:19

I would put the bulb on for 30 minutes. This will remove approximately 2.5Ah of charge from the battery which will have a capacity of around 70Ah for a 096 type when new.

You should get at least 12.5V which would indicate that the battery is at >90% fully charged.

If it drops to less than 12.5V, the battery is not as healthy as it should be.

MSS 9th November 2021 23:34

What was the measurement or conclusion in the end?

macafee2 10th November 2021 08:08

Quote:

Originally Posted by MSS (Post 2907297)
What was the measurement or conclusion in the end?

Result, undecided about the battery. The voltage seemed not to drop any further, always staying above 12v. I am wondering if the fault is on the car. I kept a headlight bulb connected for well over an hour as suggested but the voltage stayed above 12.
I have just taken the battery off charge and it is showing 13.04v.

macafee2

COLVERT 10th November 2021 15:35

The reading off charge won't be accurate.--It needs to be left for a few hours to settle.

12.57 is normal for most batteries.---:D

The very best way to check a sealed batteries capacity is to have a drop test done at a local garage.

Oh for those filler caps where you could test the specific gravity of the acid.

macafee2 10th November 2021 17:08

Quote:

Originally Posted by COLVERT (Post 2907380)
The reading off charge won't be accurate.--It needs to be left for a few hours to settle.

12.57 is normal for most batteries.---:D

The very best way to check a sealed batteries capacity is to have a drop test done at a local garage.

Oh for those filler caps where you could test the specific gravity of the acid.

ok thanks, I'll test it again in the morning

macafee2

patrolman pete 10th November 2021 19:48

An old way that the AA used to test batteries was to charge by running the engine for 5 mins , then disable the engine by pulling a fuse so that the car would crank but not start. Crank the engine for 15 seconds and listen to the cranking speed , and if it starts to drop , the battery is unserviceable . That is a live drop test and is pretty conclusive.

macafee2 11th November 2021 09:16

Quote:

Originally Posted by patrolman pete (Post 2907401)
An old way that the AA used to test batteries was to charge by running the engine for 5 mins , then disable the engine by pulling a fuse so that the car would crank but not start. Crank the engine for 15 seconds and listen to the cranking speed , and if it starts to drop , the battery is unserviceable . That is a live drop test and is pretty conclusive.

I can try that. What fuse to remove, fuel pump?
15 seconds continuous cranking seems a long time, I just timed it my goodness that is a lot of cranking

macafee2


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