[Cushman UTV Max]

Hello team, I finally got my new project home. My kids are really excited! We went through the traditional wash and cleaning. Tonight I got some time to see what was is going on. All the cells show proper fluid level. The total pack voltage is 23.3 volts on a 48 volt system. All the batteries measured just under 6 volts except 3 batteries. The three measured 0.10, -0.70, -6.0. Just for the heck of it, I put a 2 amp battery charger on the -0.70. The charger saw it as an open circuit. I am surprised by the -6.0.... The batteries were installed last year. The cart ran fine (I am told), then nothing this spring (I am told). I plugged in the charger (on board). The pack voltage showed no change. I assume this is a self protect system. Beyond the questions above, here are a few additional: Can I use a 2 amp 6 volt charger on each battery (without disconnecting them from the circuit)? If 3 new batteries are in my future, can I buy used and mix them in? I am taking the connectors off one by one, cleaning, and using a thin coat of vaseline... Thanks in advance for your thoughts and tips. Tony in Michigan