battery maintainence

So my camper co-owner and I divide up some jobs. He checks the batteries for water levels and last time he apparently forgot to put the caps back on. In trying to buy a replacement set (from advance auto where I bought the interstate batteries) I was told you can't buy replacements anymore because you don' need to check water levels any more and so there's no reason to open them (and thus potentially lose them).

Good question.  Todays batteries are made of better alloys than old batteries.  A maintenance free battery may have vent caps, but in many cases they are sealed and removing them can void the warranty.  My RV battery has cap covers, two that cover 3 cells apiece.  They are removeable and I can and do check my water levels and fill as required.  Many places cell vent caps, Amazon, eBay and other vendors on the net.  Google "Battery Vent Cap"  When  trying to remove a vent cap from a maintenance free battery, I have found them sealed, those you want to leave in place as to not void warranty.  Hope that helps.

Bayonet style is normally a 1/4 turn lock versus a push in style.  I like idea of getting off a turn in, just a matter of getting them from a source with good turn in quantities.

+2. Plenty of flooded batteries with removable caps still available. Deep cycle batteries are almost always like that. Find some off some old batteries. Wash them out to be sure they don’t have crud in them which could contaminate your battery cells,