battery problems

[abeefx]

hey guys

my fresta zetec s is having problems. 3 days ago the battery went flat, jumpstarted it no problems for the next 2 days left it for about 20 hours flat again bumpstarted it this time. currently at work ive just been onto the digital battery display and its was going up and down from 12.(4-6). when the guy came out to jump start it he checked the altenator and said it was fine. so im guessing it the battery but my car is a 56 and just under 2 years old so its hard for me to belive its the battery?? so just out of interest how can i check if somethings draining it? ill be checking the battery reading again throughout the night and seeing if it drops and trying to catch it before it drops to 12.0 IF it does. im guessing it will.with it being about 12.5-6 im guessing that shows the battery is charging?? so does that rule out a battery problem?

latest check after about 3 hours my battery is now showing at 12.3-4
this is using the incar display tester to show the battery reading not sure if thats enough to use .3 ish volts Very roughly id say its like 0.05-0.08 volts and hour loss?? if the battery was kncackerd is this about the right rate of loss? or is it too slow a rate for this and it is a drain problem?

thanks


thanks

[MagicRat]

Welcome to AF.

As you have a digital volt meter, test the battery voltage with the engine running. This tells you the alternator output voltage. It needs to be about 13.5 to 14.5 volts in order to keep your battery properly charged. If it's consistently lower than this range, the alternator is bad.

If the alternator is okay, then you cna easily check the battery. The next time you park it, disconnect the battery negative terminal and set it aside. This will isolate the battery from the rest of the car. After 20 hours (or more) reconnect the battery and see if the car starts. If the battery has gone dead, it's bad and needs replacing. Yes it's only 2-3 years old, but many OEM batteries go bad at this age.

If the battery starts the car just great, then there is an electrical drain in the car's wiring, which often requires considerable skill and effort to track down.

Finally, it is normal for batteries to show a slight decrease in voltage as the car sits. I believe the spike in indicated battery voltage just after charging (or the engine running) is called 'surface charge' and is temporary.