Batteries for Towers
FA Tower
- Battery right next to it.
FM Tower
- Battery right next to it.
MT Tower
- Battery in car across bridge on way to church.
PV Tower
- Not in PV (searched pretty much the whole map) but in CH. In the green car between Log Sort and Quonset.
Note: My guess for the OP is that a battery exists somewhere in your game. Probably underneath a hood somewhere and you may have to trek to find it and bring it back.
I did the Signal Void in Interloper (vanilla), and found the battery for PV transmitter in the hut at side of the tower, in the tilted shelf at right of the lockers in the entrance.
See other battery in the SV bunker in HVR.
The battery used for MT transmitter I found in a car in the road going for the church.
Batteries on loper only have a 1 in 10 chance to spawn in a car. It was one of the reasons it wasn’t initially in loper. Some peoples loper worlds have no batteries at all.