If it has bluetooth, then try to disable or turn off the bluetooth. That will save tons of battery life.

Otherwise, the best battery effort will come from being in a small, fully digital cell within the carrier's coverage area. In larger cells, it will consume more power, ditto for cells that don't implement the most modern protocols (eg. 1xRTT is better than plain digital, which is much better than analog..).

Other than that, the battery or handset may be defective. I had a defective handset here once, and after considerable persistence managed to have it replaced under warranty. The replacement lasts weeks on standby. Dunno about talk time -- I'm like you and hardly use it.

Cheers