On Fri, 15 Nov 2013 23:04:18 -0500, "Mike Marlow"
If you go Li-ion, voltage is not going to matter. All of the Li=ion
batteries are small and light weight as compared to non Li-ion.
18 volt Li-ion is probably lighter in weight than a 12 bolt non
Li-ion.

Only if you go with the small LiON batteries. Full sized battery - no way,
Leon.

Well, the18v Li-ion are lighter than the other 18v batteries, but not
enough so that he won't feel the weight of them. As suggested, I have
to agree that the 12v tools (of any battery type) are much lighter
than their 18v brethren and that's what I'd recommend in this
instance.

Of course, the only real solution to this problem is for the OP to go
to the store and find out for himself. It's his arms that will answer
the question of what to buy.