Could it just be the battery - has it been dropped in water or otherwise damaged ?
One problem I've seen with both (old) Ericsson and Nokia phones, is the contacts in the phone (which were springy strips of metal, folded over, the springiness used to ensure contact with the 3 or so contact points on the battery) was that the contacts in the phone could either have broken on the 'hinge' so there was an air gap instead of proper contact with the battery, or could have been corroded because of moisture, or just plain grimy.
I've sometimes taken a battery out and (carefully) scratched the battery contacts with either a small screwdriver, or something like metal wool, such that there's some fresh, bright, metal, exposed.
Similarly for the strips in the mobile, or, if part had broken off, bending what was left in half (again, carefully) using some small pliers (normally used for holding components when soldering them).
If you get no joy at CPW, you might consider finding a replacement battery for the phone, on Ebay, say.
You don't mention which phone it is - if you do someone else who has had the same phone may be able to give you a much better answer, as they'll know what worked and what didn't! Good luck.