Mex,
Try this procedure before replacing batteries: Find polarity on battery pack. Attach (-) phase wire on (-) battery pack terminal. With battery charger turned up high, scratch a (+) phase wire across battery pack's (+) terminal. You want to see a spark but don't want any excessive current into the pack. Scratch across it. Charge battery pack as per usual.
I've used the above tactic on a few rechargable sets that wouldn't charge or held poor charge capacity. It has worked nearly 100%.
An alternative to fixing old battery powered tools is to buy Ridgid brand at Home Depot. They offer a lifetime warranty on tools, batteries, and charger. I've enacted the warranty on a bad battery pack. I had a new one in hand within a few days, no charge.
