Please Help me!!!!!!!!!!!!!!

I jailbreak my iphone to 3.0.1 and after that I unlock it and install software az before I had them. when I used my Iphone until the battery finish I connected to my computer for charging but it charge only near 50% and I kept it for long time in charge but it charged less than and less than until it dead. /i disconnected and connected to plug and it's happened same.
one more time I reset my IPHONE and jail break again and unlock but it charged full like past. after I used it it's happened again.

Please help me I can't use my Iphone forever \
regards
AMIR