Dave
Try resetting the SMC:
Shut down the Mac.
Plug in the MagSafe or USB-C power adapter to a power source and to your Mac.
Using the built-in keyboard, press Shift-Control-Option on the left side of the keyboard, then press the power button at the same time.
Release all keys, then press the power button again to turn on your Mac.
Anonymous
Hmm! Get a battery about $99
chrisjbsc
Replace it.