Is your feature request related to a problem? Please describe.
There was this handy feature in IC2 when you could have small batteries with you and charge devices with right-click. And there is no low-tier batpacks (only the Lithium-Ion Batpack). So you're stuck with your portable devices at the beginning without portable energy cells.

Describe the solution you'd like
I think, it's good idea to copy this ability to use batteries directly from IC2.

or is it easier to have it if its in the off hand it charges the item in hand?

or is it easier to have it if its in the off hand it charges the item in hand?

I guess it is.