Flat Battery Fiesta diesel

[stuartdm]

The battery on my fiesta is flat and not charging, however, once the engine is running the electrics work fine. How can I tell whether it is a dead battery or a broken rectifier.

 

[joe-90]

Disconnect the battery overnight.

If it goes flat - it's the battery.

If it only goes flat when you reconnect it - it's a blown diode.

 

[InTheBeginning2007]

Get a volt meter, or borrow one. 13Volts or more across the battery when engine running, then it is charging. If it is less, suspect alternator.
Also check water/ acid level in battery and top up (if it is an old style batery that can be topped up.