Battery voltage questions re ACR

[stradman]

Hi All,

I would like to know what sort of battery charge one should have. My car is 18 months old and only 1500 miles. My original 18 month old OEM battery in situ with connections on but ignition off, shows on my voltmeter 12.5v. When you put it on a trickle charger it is showing 12.9volts. I have my suspicions however that the battery is not sound, as after say a week off charge when you turned it on it was slow to turn over, and on a couple of other occasions even after a good drive and then leaving it about a week(always indoors in a dehumidified garage I might add), it wouldn't start and needed a booster start. So I bought a brand new battery today with the same CCA but with 52Ahr instead of the stock 35Ahr. I checked the voltmeter on this new battery when I installed it and it showed 13.15 volts sitting in the back with connections in place but ignition off. When I put it on trickle charger it shows 13.7 volts. So it seems there was quite a difference with the OEM .
I have my suspicions that the battery was my problem at my first track day event when my engine shut down along with a CEL light , and also a ETC light as well. As I was sitting there idling cooling off after about 3 hot laps the voltage suddenly dropped from 14.6 to 11.2v , idle went lumpy and engine shut down. You could then only start it for about 15-20 secs even then in that brief start up, idle was lumpy and voltage was still low. Diagnostics showed a P0560 code or systems voltage. So I was wondering what you guys thought about the battery voltage.