The only way to stop unused lead-acid cells from sulphating is to use an isolating layer to protect the lead from the acid. Traditionally mercury--but this was banned ages ago in western countries. After five years I would suspect there was such a depolariser at work--that seems an awful long time for a battery
to remain in good condition without sulphating.
Batteries of the deep cycle type are designed purely as house batteries. They have low amperage outputs and heavy plates--and I suspect the Rolls battery
is one of these. They are purpose designed to be charged and discharged repeatedly over long lifetimes --and are not designed to start engines or deliver heavy loads beyond their normal output, usually about fifty amps or less. Enough of them connected in parallel will start an engine
, but for those purposes separate starting batteries are better--having thin plates of large area and designed, not for sustained use, but for a quick heavy load followed by a quick recharge.
Some sailors fit two alternators to the diesel--one for the start battery and one for the house cells. This charges both sets at once--but house batteries of the heavy lead plate sort need to be charged more slowly. If you use the diesel
a lot, say to pull down a freezer
plate, one with a smart regulator
could probably handle both banks.
cells were originally designed for the aircraft industry as starting batteries for big engines and turbines. The technology of having huge amperages deliverable over long-ish starting times of up to twenty or thirty seconds makes AGM
batteries for boats sufficienct in capacity to serve as both house cells and starting batteries--but they are more than double the price
of standard flooded cells.
I suspect the life of AGM cells could be less than that of the old deep-cycle house batteries--which in country power installations and small telephone exchanges could last up to twenty years. Much less in marine
The life of any battery depends on how it is used, how often discharged and recharged, how deeply discharged it was, the rate of charge and discharge, the maintenance
if any, any contaminants (never use watermaker water
in a marine
battery, always use distilled water) and how knocked about it gets. Internal short circuits are a big killer of batteries. A smart alternator
will also make your batteries last longer--it will give them a variable charge rate cycle and an equalliser charge. Ordinary alternators do not do this--you have to equalise the cells yourself. Use the unregulated 24 volts or so from a solar
panel for a day once in a while.
The good thing about gells is they are not vented, instead of losing the gasses they employ catayltic reconversion of the gasses to water
again which is re-absorbed into the gel matrix, as do most low maintenance
batteries. They will work for a while completely submerged, or even a long time provided the connections are wrapped in polyisobutadeine tape which consolidates to form a waterproof rubber shield.
Once one could buy dry charged batteries which one could store without the electrolyte almost indefinitely. Maybe one can still order them this way. When one neded them one added the electrolyte and gave them a quick top-up charge--so it was possible to carry spares for a long time provided the acid did not leak out of the bottles.
These days if you can not buy a spare battery dry charged with separate electrolyte one can do it thenselves--you charge up a new battery, then remove the stoppers and invert the battery over a bucket--the rectangular mop type is best. Let it drain completely, then wash it out with several changes of distilled water, letting it soak for a while before emptying each time. Keep this water and label it for use in topping up the spare battery if you have the room, otherwise get rid of it after neutralising it with a teaspoonful of baking soda. Finally let the battery dry overnight, then replace the stoppers. Bottle the electrolyte and label it. Store it in a wooden or plastic box, padding it to prevent movement.
You now have a spare battery which will be ready when you need it--years later. Give it a quick charge and it will be as good as new.