If your battery was left in for some time then it could be too late.
If you've not taken a phone apart before then be warned it is tricky and easy to damage. You really need a workshop manual. I posted a link to one for my SGS1 and it may be similar.
Jewellers screwdriver set
Small brush ( electric shaver cleaning brush, or toothbrush may do)
Phone case opening tool (fingernails or plectrum sometimes suffice)