my bros mk2 fiesta battery went dead on his car after driving it so we fitted a new 1 but after driving it the new 1 also went dead.we run a voltmeter and the battery is reading 12volts.when we start the car it goes up to 13.5 volts but under load it goes back down to 12.5 volts any ideas what could be wrong with it by the way its a 1.4 efi

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blunty

Alternator sounds shagged. Under load it's not providing enough current to charge your battery when all systems are being used. Have a double check of your belts and make sure they're tight enough (not too tight though!).

It should be reading 12-12.5 with ignition on, over 14 when the car is started, and it shouldn't drop when you boot it.

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