Does the pump work now it's cleaned up ,back in the workshop where there is mains power?
Have you measured the starting and running current?
Do you have an inverter yet?
I've recently purchased 2x Halfords leisure batteries which are made by Yuasa, the decision to go for there was purely that it was collection from a local shop and the same if any warranty issues arose.
I only use sine wave inverters, so can't comment on modified ones.
Fuses in batteries etc will be required too.
It runs and pulls enough vacuum to activate the pulsator but doesn't extract milk that efficiently. Once I get the two broken vanes replaced hopefully it'll work like new.
No I haven't tested current yet, I'd need to dig out a power meter.
No I don't have an inverter