For what it's worth, every so often I perform a practice pull start on the engine. Using the law written by a certain Mr Sod, this has ensured my battery (bought at milliseconds' notice for £45
from a Kwik Fit near my location at the time) has so far not failed me!
For the record, I have since discovered my original 80AH deep cycle batt had nothing wrong with it, the problem was corrosion on the isolator innards, so when "on" it had a nice resistive lump of corrosion between the terminals. Ironically the emergency purchase is about half the weight of the old one......
All joking aside, if your engine(s) is / are old school 2- strokes then once they are spinning all the battery needs to do is smooth the suupply to your electronic toys & store some electrical juice to crank the engine next time you start.