Dodgy Battery?

Hey, ive been having trouble with my battery, im pretty sure its holding its charge but the power seems to go really fast... could this be a dodgy alternator? or something shorted somewhere? it will start fine after a charge and for that whole day, but the next day it just goes... i changed the drivebelt as it was old and knackered.. how can i test the alternator? thanks josh

The only way to properly test an alternator is by using an ammeter. But you can do a rough test by observing the voltage output at various stages of running. With the voltmeter across the battery terminals, look for these voltage (approx):

Engine not running, no electrics on: 12.4-12.8 volts
Engine not running, headlamps on: not less than 12 volts
During starting engine: more than 7-8 volts
Engine running and battery light out (might have to rev it), just after starting: 12.8-13.4 volts, or thereabouts.

you need to put a volt meter on the circuit when the cars running to see if its charging properly, should be a reading of around 13-14v

It sounds like the battery is knackered to me though, even if it wasnt charging it should last longer than a day, if the alternator goes then you will normally get the battery warning lamp glowing back on the dash, but not always

Take it into a kwik fit or somewhere simmilar, your not obliged to buy from them as they do "free battery check" which includes the charge rate etc

this time of year often kills battery cells, constant use of lights and heaters for short journeys and the cold can speed up killing an old battery off