[uoaei]

Nitpick: it's sap the battery, as in sapping energy.

[Onawa]

I think both 'sap' and 'zap' work in this context, and zap might be the better option because 'sap' can have the additional meaning of moving the energy somewhere else, whereas 'zap' can just mean to remove in general.

[uoaei]

"zap" has never meant to remove anything, in general, where are you getting this?

[Onawa]

https://www.merriam-webster.com/dictionary/zap

zap: 2 of 3; verb zapped; zapping; zaps

transitive verb 1a: *to get rid of*, destroy, or kill especially with or as if with sudden force

I was using the "to get rid of" portion of the definition.

[uoaei]

That implies you've detonated or otherwise destroyed the battery, not merely drawn the energy from it.