Hi all

i think I know the answer but wanted to ask anyway. 2009 hatch STI, only gets used at weekends occasionally, only 50000 on the clock. The battery was flat last week (or rather didn’t have enough charge to turn over but all electrics worked after been sat for about 3 weeks) so I charged it up, put it back in and when I went to start it the next day, it hesitated a little then sprang into life. I measured the voltage when idling and it read 12.4v. In any other car I’d look at the alternator but wanted to check if there was any other culprits? I’m assuming the battery is original so maybe that? I measured straight across the battery rather than between positive and an earth point, but that shouldn’t make a difference. Any thoughts greatly appreciated

 

With engine running with some load, the alternator should be charging as per workshop manual info below:



You should also check or have your battery checked for Voltage and its indicated CCA (Cold cranking amps)

 

New battery

 

Hatches seem to have a drain on them; my spec C hatch goes through a battery a year, but it is for a Micra.

 

Given the age and limited usage of your 2009 STI, it's probable the original battery needs replacing. While checking the alternator and cleaning terminals is wise, a new battery could be the key to reliable starts.

 

Thanks all, I’ve changed the battery, so see if that fixes the issue. The old battery was reading 9.4v when I measured it after been sat for a week so looks to be the issue. Now to work out why my BMW is drinking a litre of oil every 3000 miles!