battery flat every morning

[stephen2504]

how can i tell if the battery is broke or the altenator

[dannywells]

the alternator can be tested by 2 methods
first if the alternator isnt charging you should get a bulb telling you so in the instrument cluster - however this doesnt always happen - to tell if the bulb is blown you should get a bulb lit up, perhaps with a battery symbol when you start the car, the bulb should then go out indicating the alternator is charging

Allternatly you need to check the voltage at the battery when the car is running - you need a multimeter to do this - check the voltage is above approx 13.8volts if its below this then the output should be checked by a garage as to why this is occuring as a number of factors could cause it, although most likely worn bushes

[ray bush]

Yes it could be the alternator ,but i also had a boot light that stayed on ,that drained the battery every night.Just close the boot and flap the seat down at the back and have a look,at least it illiminates that area .

[Hammer]

Face a wall with your headlights on so you can see them shining on the wall and rev the engine. If your lights get brighter when you rev, then the alternator's OK.

[dannywells]

not really an ideal test regards headlights, they may well get brighter, that doesnt mean the alternator is outputting enough power to charge the battery and a good regulator should mean the lights shouldnt get brighter at all when you rev the engine

[Gef]

If the car restarts later in the day (after you have driven to work) then it is the battery and not the alternator.

[dannywells]

that above answer is completly untrue

[Gef]

danny, please explain.

[dannywells]

i dont need to explain

'If the car restarts later in the day (after you have driven to work) then it is the battery and not the alternator.'

if your car starts after youve driven to work - you have a faulty battery!!?? i think ur a bit mixed up there

[homer75]

An autoshop will put a high discharge tester on your battery for you and tell you if it's knackered. They would also check your alternator output - only takes a few minutes.

[stephen2504]

thanks for your answers

[diode dug]

some auto shops will sell you a battery, then next week sell you an alternator. high rate discharge testers dont locate build ups between the plates or self discharge, the age of the battery tell alot.

A cold snap will show up loss of performance in a battery esp if its on its last legs, it could have started the vehicle all year the one cold day, click click click.

its worth renewing your batter (diy) as a matter of course as its often far cheeper, check boot lights first. The the alternator works better in cold but the the battery dies.

try...
Charge batter to full state via external charger vehicle now starts with ease, now turn head lights on for 10 mins (approx) with enging off. If car fails to now start or wow wow wow click..renew battery, its going to let you down anyway.

A good battery voltage should be around 12.6v off load after around 3 hours of none use and 13.6v to around 13.8v after the alternator has cut in just after idle speed (give it a rev) you can hear the alternator sing when it cuts in if you know what your listening for.

hope this helps