I have two VX-4400 Samsung phones (spouse and mine) and had the same problem with both of the like others on this site! Wouldn't work on charger - brought it in and they said I must have got it wet because water sensor on back of battery indicated water. I know it did not get significantly wet. Wanted $20+ to replace. There were several people complaining of the same problem when I was in there and everyone was mad. Appears to be bad battery design - tech says even drops of rain can ruin it while its attached to your hip.