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Battery voltage and potential replacement

S

Steff

Trainee
Joined
16 Jan 2015
Messages
96
Hi,

If I know I'm not going to drive my 3.4 for a week or so then I plug it into a CTEK MXS 5.0.

Recently when I do this, the CTEK will intermediately stop at stage 5. The description in the manual is 'tests if the battery can hold charge, checks if voltage drops to 12v, batteries that cannot hold charge may need to be replaced'.

It doesn't do it every time but often enough to conclude that the battery isn't holding charge.

The question is, how low can the voltage go and the battery still operate fine? I drove it on Monday and it seemed to start fine. Just wondering if I need to replace right away or just do it as soon as it becomes slow to turn over.

At the same time, I want to avoid the hassle that seems to go with a completely flat battery so would rather replace ahead of that.

Thanks
 
Have you tested/had the battery tested properly rather than rely on the charger?

I would do that before buying a replacement.
 
Thanks, just put a volt meter on it. It's showing about 12.5 normally, just over 14 when running (so I guess the alternator is fine) and it drops to about 10.5 when I start the engine.

I'm not sure how low it should go when I start, I know lower single figures is bad but is over 10 fine?

Thanks
 
10.5 volts on cranking is what a good battery should read .

14 volts running is fine but you really need to have a voltmeter on the battery .. turn lights and any heavy electrical loads on then see what it is at idle .. anything less then 13 volts and your into a worn alternator.

12.5 volts is again a sign of a good battery .

The only other check would be a dedicated battery tester or an acid check which cant be done if the battery is sealed .

If the battery starts the car after 4-5 days without being used in the mean time or connected to a charger then its fine.
 
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