Battery

[Sandun]

I went 1/2 Km on my MM1000 car , then Stop the car and check the Battery Volt ; It was 12.51 V, - After 1 or 2 hours( car ,not start again & not run) I re check the Battery Then It was 12.38 V - Why ??

[Neil MG]

Old battery?

Courtesy light on? Or maybe the drain from trying to start. Also if the battery is very dirty! Read this:

http://mgaguru.com/mgtech/universal/ba101.htm

[Sandun]

Battery is New one

[bmcecosse]

So - something is draining the battery. Take off one of the terminals - and then lightly 'touch' it back to the battery post - do you see a small spark/hear a little 'crack' ?? Also charge up the battery - it should be reading 14 volts when charging from the dynamo - then disconnect it and leave overnight - what volts then ? Won't be 14 but should be perhaps 12.8 something like that.

[Sandun]

Do you say , It is normal ? or Bad Battery ?? What is the Meaning of "draining " Bad Battery or Must Charge ?

[bmcecosse]

'draining' = running away, emptying

[rayofleamington]

When driving the car, the battery will charge (voltage applied 13.5 to ~15 volts depending on alternator / dynamo and how well it is controlled and what power the vehicle 12v system was using).
During charge the battery voltage level rises, and it decays on a decreasing curve after the charge voltage is removed.
Therefore if you read battery voltage straight after driving and again after a few hours - a reduction is 100% normal.

The voltage levels you mention sound slightly low. This may mean your new battery was not fully charged (sometimes they sit on a shelf for months!!). If this is the case, don't worry. You could charge the battery with a mains charger if you are worried.

If there are other symptoms (e.g. battery goes flat after a few days) then that's a different issue.

[Sandun]

Thank you so much