I would request that similarly to the way Rechargeable batteries, when you right click with them, send their energy to another Non-full chargeable item, Bat-packs as well as Disposable batteries ought to be able to as well.
The disposable batteries would, when right clicked, remove one of them to recharge 1k energy. Without this feature, Even with the extremely easy method to make them, I would not do so, as they are not currently any more convenient than rechargeable batteries.
As for the bat-pack, It would act exactly like Re-batteries do when right clicked, aside from having 60k energy available. This is not exactly necessary, however, It would be useful to me, as a E-Jetpack user, To be able to recharge my drill without having to take my jetpack off, and mining about 60 blocks, because that is rather dangerous when I use the Jetpack to avoid falling damage as well as to *jump* if I hear a creeper.