batterey

[hench]

my batterey light has just started to come on when i rev the engine but goes off when not reving any ideas why or do i need new batterey

[homer75]

You need to check the alternator output by putting a meter across the battery terminals also high load meter to check battery condition - a decent auto shop will do this for you for free.

[wallis1007]

Your alternator is about to die!

[clancyblob]

Could well be the alternator not charging the battery. It's not a cheap thing to replace (�50 - �120 new, depends on make of car), but quite easy to do. There is a slim chance that the belt which turns the alternator is slipping on it's pulley, a diy mechanic can check this in 5 minutes and tighten if necessary. There is also a small chance that an electronic circuit that allows the right charge into the battery is at fault. A half decent mechanic can also check that out for you. Most cars under 10 years old with have a little black box somehwre which has this circuit. Changing it is quick, but it can be a pricey little box of chips and circuits - again depends on make and model.