From the manual:
A little trial and error will show you what is the optimum setting for the situation.
I guess you can't expect much from a $20 Walmart drill.
They already have a backpack battery for the X2 tools.
http://www.makitauk.com/accessories/batteries/li-ion/bl36120a-36v-battery-backpack.html
No reason they might not continue down that path.