I would have bought the A520 when I purchased mine, but I could only afford the 510 at the time.
As for the battery problem, I can take a couple hundred pics before I need to swap batteries and I use manual settings all the time, which reduce the battery life.
Are you using NiMH? Have you "refreshed" the batteries lately? Sometimes a low charge will drain the battery faster. To refresh, your charger may have arefresh setting or you couldjust keep the batteries in a device with the power on until they die completely. I always keep a fresh set fully charged at the ready.