Mixing Batteries- For a quick test ONLY

[Ronman]

I am attempting to revive my 2000 36v Series TXT. Last time I used it I took it off the charger, backed out, put it in forward and it went dead. I pushed it back into the garage and it has sat there for a year. I never knew if it was my batteries, charger, motor or something else.

I want to get it running and upgrade to new controller, f/r, etc. and possibly 48v. However, I don't want to buy new batteries until I know it's just the batteries. I took the charger to the golf course the other day, plugged it one of their carts and it is working. They wont allow me to use their batteries in my cart to test.

I have managed to get 5 batteries over 5 volts with only 30 minutes charge each. The last battery is completely dead.

So, my crazy idea is this... Can I pull the dead battery and the one next to and drop a 12v from the boat in their place? I only want to hit the pedal and make sure it goes forward and reverse, never leaving the garage. Will this hurt anything? I'm not going to try and charge, I'm not going to take a spin.