Odds are your battery is ruined due to lead sulphation as JW pointed out. Your never going to get a full charge. Seems to be fairly common problem with P-cars. Probably due to long periods of sitting. Keep in mind, even if you disconnect your battery, it will still slowly loose charge. And when the battery voltage goes below a certiam amount, lead sulphation starts to occur.
I've been trying to revive one of my sulphated battery's with a pulse charger with limited success. The only real solution is a good trickle charger and keep it topped off.
Here is a great FAQ about battery's...
http://www.uuhome.de/william.darden/