X-Roughneck said:
So you are saying a every now and then charge coming from a Old School Battery Plug in charger is better that having a 100w free panel on the fence constantly trickle charging... from a pure battery Life stand point?
Here's the definitive answer for that - it depends.
When batteries are in their "prime", and in a cool climate (winter), self discharge is little and a shot every six months will bring them back up. When factored into the "noise" of all the other operational nuances of how an RV battery is used over it's life this becomes essentially suspended animation where the clock is ticking but the chemical activity is minimal. But technically the battery is sitting at some state of charge less than 100% and for an extended period of time so it's not "ideal".
Constant trickle charging has the advantage of keeping the battery at 100%, 100% of the time. This minimizes the slight chance of sulfation an inactive battery might see. But, the actual voltage or charge profile used might not be "just right" for the battery topology and temperature, and could cause a bit of water use which if left unchecked can result in a dried out plate and ruined battery. If the "trickle" is a bit more than a true trickle that extends for months at a time it can cause irreversible damage to the grid paste ("paste shedding") so there can be too much of a good thing.
In my opinion the best option is how many of the mains powered battery minder/tender products do it. They monitor the battery voltage and only give a shot of juice for a prescribed amount when the battery actually needs it. This eliminates the variables of temperature and self discharge conditions and there's virtually no water use. Maybe there's some solar controllers out there that do this which would be the best of both worlds.
Not factored into any battery maintenance you usually see published is the issue of electrolyte stratification. For any idle battery this is a problem and will contribute to declining capacity over the life of the battery if it sits unused a lot. The remedy for that is to either physically move the battery around (drive the vehicle) which stirs the electrolyte or provide an equalize charge which will generate gas and stirs the electrolyte from inside. Once a month would take care of this but I think the prevailing opinion is more people would cause damage to their batteries by the over application of equalize charges than the damage caused by stratification, so just let the sleeping dog lie. I've seen some converters and solar chargers with an equalization mode and it's a standard protocol in stationary battery banks. With the preponderance of other deleterious issues at play in RV service, stratification is low on the list but if you're off into the weeds debating the subtleties of trickle vs boost maintenance you might as well cover all the bases.
At the end of the day, even a battery stored "perfectly" is going to fail eventually. They're degrading from the minute they're made and operating them successfully is just an exercise in managed decline. In the grand scheme if you just do "something" you're way farther ahead than if you do nothing, so run 'em hard, charge 'em up and get what you can while you can because the end is always nigh. If you manage to use them up before they give up, you win.
Mark B.
Albuquerque, NM