Adding to the other good replies- I the back of handy magazines, I've seen advertisements from companies that can custom make a battery pack for any need. Check Family Handyman or similar woodworking mags. In fact, I;m sure you could search the net and find the service. Pretty awesome, because you can fix any item, even if batteries are no longer in stock.
If you are handy you may be able to open the case in order to see the cells used. Then order the generic cells and replace them yourself.
ebay,craigslist, garage sale,home depot,lowes,ace,grainger, secondhand shop, sears, or the actual companies website like craftman,black and decker,ryobi ect.
ebay,craigslist, garage sale,home depot,lowes,ace,grainger, secondhand shop
Google " 'brand' drill battery" and take your pick.
+1.Home depot, Lowes, Sears,and single purpose battery shops may have your model also. (single purpose battery shops can be found in your local yellow pages or similar. We have at least one in Cleveland, and I'm sure they exist elsewhere
tell us the brand and model. will do some research
You could try direct from the manufacturer(may be a bit expensive), or try ebay(may be a bit cheaper). I hate to recommend google, but type in the battery model number followed by replacement and see what comes up. Worth a shot.
Ahh well that depends if it is a craftsman try your local Sears store. If its any other, assuming you live in the states, try Batteries Plus. If they don't have it in stock they will order them for you. on sears just type in the search the batteries voltage eg. "15.5v Batteries"www.sears.com/www.batteriesplus.com/manufacturer/50-0/Cordless-Tool-Batteries.aspx