Camera won't work

Camera won't work
OKAAAY!!!

I put in a brand new battery and all seems fine. But why does the old battery show charged when I put it in the charger?

What type of battery is it ?

NiCad ? Lithium ? Lithium Ion ?

If it's a NiCad it sounds like it's suffering from extreme memory effect. Shows full but the bucket of electrons is extremely small indeed so when the camera wants some it dries up faster than a thimble full of beer at a German lager festival.

Lithium Ion cells don't suffer from the memory effect but they don't like long term storage. They are also very sensitive to temperature. Especially low temperature which affects their performance geatly.

NiMh (Nickel metal hydride) suffer from similar problems to NiCads but not as bad.

This may sound silly, but it often works to revive a memory-bound ni-cad.

Freeze it overnight in the freezer compartment of your refrigerator - you wanna get it down to around or slightly below Zero Degrees Farenheit. After a good 8 or 10 hours of freezing, remove it and rap it lengthwise smartly on the countertop a few times, rotatin' it slightly each time so essentially all sides of the battery get a strike. 4 hits oughtta be plenty. Immediately put it into the charger - with the charger configured for slow charge if thats an option - and charge a full 24 hours. Remove the battery from the charger at the end of the period and, using a suitably voltage-rated lightbulb, fully discharge the battery. Use an incandescent or halogen bulb rated for a voltage at least equal to but not much more than twice the battery's rated voltage. A 9V halogen bulb works real well for batteries anywhere from 3.5 to 9 volts. LEDs don't have enough draw to drain the battery quickly enough. Just as soon as the lightbulb almost goes out, just a dim glow, repeat the freeze-charge-discharge trick one more time. Be observant, you don't want a heavilly discharged battery connected to a load very long. If the battery can be brought back to life, that'll do it.