(Not a repost; previous deal expired, but now the earlier price is back.)
Amazon has the DeWalt DCA2203C battery adapter kit for $130.04, and it is eligible for the "$20 off $100 DeWalt" promotion, for a final price of $110.04. Promotion is automatically applied at checkout if the seller is Amazon
. If the page doesn't say "Ships from and sold by Amazon.com", select from the "Other sellers on Amazon" box (or add a "smid=ATVPDKIKX0DER" field to the URL).
This kit contains an adapter that allows one to use (some of) the newer 20V MAX Li-ion batteries with (most of) the older 18V tool line, two DCB203 batteries, and a 20V MAX charger.
For reference, most outlets are carrying this kit for $140-$150 and just a two-pack of DCB203 batteries for $120. The kit has not been on the market long enough to see a truly
slick deal yet, but even without the $20 off promo it is near the lowest price according to CCC.