Woot has a two pack of the compact (1.7 Ah) POWERSTACK battery for $82.99 with free shipping for Amazon Prime members.
They are also selling them as singles for $44.99 each.
Other POWERSTACK options in kits with chargers:
https://tools.woot.com/offers/dewalt-dcbp034-2-20v-max-1-7ah-battery-2-pack-2
They are also selling them as singles for $44.99 each.
Other POWERSTACK options in kits with chargers:
https://tools.woot.com/offers/dewalt-dcbp034-2-20v-max-1-7ah-battery-2-pack-2