A couple of things I'd add, are you using proper GC-5 batteries in the machine? If yes, as for load testing, you can't load test those batteries with automotive type resistor coil testers, those batteries will laugh at those testers, you have to using a carbon pile or equivalent load tester to suck the juice out of those batteries. And for the charger, yes, the 3 stage is better, especially if you don't use the machine daily. The three stage chargers will do the bulk stage, bringing the voltage up rapidly at a high amp rate, then at about 85% charge they switch to absorption stage, reducing the amp rate to gently bring it to full charge, then they switch to float to maintain full charge. Most factory fitted chargers only do bulk stage and absorption stage. Once it gets fully charge they turn off, they don't do maintain float, have to unplug it and plug it back in to maintain charge with those type chargers. If you use the machine daily and recharge daily those chargers will work fine. But if it isn't used daily and does storage/idle time, 3 stage chargers are a better choice.