Battery maintenance

hobbssb wrote:
...So, unlike cell phone batteries that do best with nearly complete discharging...

And just a reminder that the old discharge your cell phone battery rule applied to NiCad and NiMH (Nickel-Metal Hydride) batteries. Modern Lithium Ion batteries don't have that 'memory effect' and provide optimal life with shorter charge cycles around 85% SOC (state of charge), although they are tolerant of most usage patterns except overheating.

An email response from Interstate said that the life of a deep cycle battery will depend upon how much discharge occurs in each cycle.
100% deep cycle = approx. 300+ cycles
50% deep cycle = approx. 1000+ cycles
25% deep cycle = approx. 2200+ cycles
So, unlike cell phone batteries that do best with nearly complete discharging, deep cycle golf cart batteries will last longer with less discharge - over three times longer when dropping to 50% vs 100 percent.
Interstate also reinforced the idea that sitting for any period of time completely discharged is very hard on a battery.
It is also possible that our batteries were prematurely aged when we purchased the RV. The dealer was located in an area that has very hot summers, with many days over 100°. If the RV dealer did not keep the charge up in that hot weather, the batteries were doomed to begin with.

Golf cart batteries in normal weather, well maintained should last 6 or more years.
One of the worst things for a battery is to let it sit in a discharged state.

Yes, we try to use the battery disconnect, but in all honesty, twice we forgot to disconnect.
When we got the replacement batteries we noticed that both old batteries were slightly bulged out on the sides. Is the bulging significant?

When you say sit, are they still connected to the van? If they are fully charged and you have a disconnect switch (and use it) they should be fine for that length of time (2-3 months). But if they are still in the van and connected to the circuit, then they will draw down. Even deep cycle batteries don't like to be discharged and left to sit.

You should get more than two years out of the batteries.