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The 7AH batteries are 6" by 4" by 2.5" and weigh quite a bit. I use them on a cord because they are just a little too heavy to mount at the end of the drill. The 3AH batteries come in a lot smaller at 2.5 by 2.5 by 5.5" and a lot lighter and are no heavier than the NiCads that came with the unit. Answering Steve's question here, I charge them with a two-stage 1A float charger I got that is designed specifically for gel cells (different rates for basic charging and float charging). It cost me $10 at Allelectronics. I'll bet Harbor Freight has one cheaper.
The float charger is used to to keep the battery topped off. I have a 33AH wheelchair battery that my battery powered sump runs from and I keep the float charger attached to that most of the time. Occasionally it's pressed into service to charge the drill battery. The float chargers put out just a trickle once the battery reaches its full charge. I'll post the model number of the charger when I get a moment.
-- Bobby G.