99 Sub. with clicking noise and no elec.

I noticed a few people had the same problem as my wife had today with our burb. Got home from work and opened the truck door and it was clicking like a speed freak sending morse code! I started cleaning battery cables and after finding out it would not hold a charge, I took the battery to Sears and put a new one in and as soon as I hooked it up it was...... Lights, Locks and action. Started right up and had full electric power to everything. Hope this helps somebody out there. Sometimes it is just a simple thing.