If you have an S2000 processor board that keeps power cycling when you turn it on (the red LED flashes on the front of the board), check the voltage of the green NiMh battery. It should read about 3.6v. If it is not, it can be replaced with Happ PN 49-0860-00.
You may notice that this Happ replacement battery is a bit taller than the stock battery. Be careful not to tighten down the memory (daughter) board too much over the top of the battery as it may get damaged