You can always full charge the phone with 5 to 6 hours . Re factory reset and clear cache. Then put custom roms some roms are good battery life roms, unlike google my nexus s 4g is new and i have it for 2 days. Day 1 last me for about 7 hours and so far it last 1 day and 18 hours. Just check for developers option and put background process limit  click and put no background process and problem should be solve.