testing device

Hi, I'm new here, and hope to find some new Bass friends. My problem at the minute is that I picked up an abandoned P bass in a roadside throwout. It needs some love and attention, which it is getting, but its electronics are not good, and I am trying to get them working again. The electrics...

Does anyone have any idea of a process to check the batteries inside the bass that is set up for 18 volts???? Dual 9 volt batteries wired in series. I have 18 volt systems in my Spectors and would love to find a way to check them, without having to remove the batteries. The system uses a 3 way...