It appears genuinely challenging to find batteries for this (It’s a discontinued model). If anyone knows the specific type and voltage, I’m curious, and perhaps someone else is too. If I could find one, it’s a good deal for the tool.
Amazon has assortment of official Hitachi batteries that fit or you can buy the offbrand lithium ion’s for a 1/3 the price both work fine as long as they’re 18 V post type.
The drill comes with the universal charger for the batteries. The batteries for this are number BCL 1815 for the lithium ion but the NiCad batteries work with this drill as well.