We have 50 2012 EZ GO RXV´s. In the first wave of battery failures we got about 100 batteries on warranty because we are very hilly and the contract said 5000 kilometers ( 3000 miles ) under warranty.
Keeping them clean and topped up is obviously very important.
It was a bit difficult under warranty because the EZ GO dealer was putting new batteries with old batteries. It is best to put equal strength batteries together as a weaker one will hurt the new ones.
We have been through our second wave and have replaced all 200 again.
We use an hydrometer brand called Ferve model F-425C
http://www.ferve.com/en/f425.htm We are in Spain and they cost about $7 each. I am sure there is something the same in USA. The hydrometer basically tests the specific density of the water telling what percent H2SO4 remains. It has been a while since I organized it but I think under 50% reading and out goes the battery.
We group batteries of equal strength together as often as possible without breaking the back of the mechanic.
Un saludo Michael
Marbella Golf Country Club