My car battery seems to go flat quickly. If I do not use my car for 2 weeks then it will not start. Also, if I leave it with the tiny map light on, it goes flat overnight (Not even enough juice left for one crank). What might be causing this?
I can't think of anything that would drain the battery while the car is off, except for the alarm. I seem to have noticed that it goes flat more quickly if I leave the alarm not-armed (but I haven't scientifically checked this).
I tried measuring some voltages. After charging on the charger, the battery was 13.25V . When my car is idling, it is 13.92V . After leaving the car overnight, the voltage was 12.62V . When idling after that. 13.92V. After a 5-minute idle and turning the car off, it was back down to 12.65V. While idling, the map light causes a voltage drop of 0.05V .
I haven't tried checking the voltage immediately after a long drive, to see if my alternator is working properly (I was going to but my multimeter battery ran out :/ )
The battery is of the smaller kind physically, although I don't see why this ought to make it go flat any quicker. The only devices I have are a 50W stereo, OEM lighting, and a boost gauge.
The battery has had this go-flat-quickly problem ever since I bought it.
The battery has a coloured spot on the top that's designed to indicate whether it needs charging or not (green = charged, black = flat, clear = needs water). The spot is a faint green most of the time. It used to go clear as soon as I tilted the battery in one direction by about 3 degrees, but I filled it up a few weeks ago and it doesn't do that any more. (I'm not sure how that works though, because the 6 cells are all separate so how can it indicate them all?)
When I put the flat battery on the charger, it indicates 'fully charged' on the charger for about 5 minutes, after which it resumes normal operation. I haven't seen this effect with any other battery I've charged. What does this mean?