Woodworkers Supply

I purchased a 20 volt lithium battery tool set ,jig saw,circular saw,drill,driver,charger and three batteries. this was about a year and a half ago. Since then I have replaced the battery 2 times. Now another batter has gone dead. The people in the store have no idea why they go bad.It cost $90 for a battery. I do not see the tools in the store any more. Can you help me with the problem. I have called every one on the sears list and they just pass me around. 20 volt lithium-ion model no. 320-2**** part s0929v032401

Help please

vluitgaren@***.net