Everyone has their own opinion on battery maintenance
, & advice that works for one person might not work for another without knowing the EXACT state of the batteries cells.
Certainly one thing is clear, GEL batteries require a lower charging
float/equalise voltage typically 0.25 to 0.4v less in a 12v battery than lead acid (not as reported above). Whilst GEL & AGM
batteries are very popular given that they are maintenance
free & in the latter case light, most people still regard the good old lead acid full traction battery for boats as they can be charged hard & fast, last 5-10 years, but do require regular checking/topping up of electrolyte.
Most modern switch mode four stage chargers have adjustements for the type of battery you are using, some as many as five different modes. Make sure the charger
is set to match the batteries & use the same type within a battery bank.
If a cell dies it often does so with a short circuit. In the case of a 12v battery this means the remaining three cells share the charging
voltage of four & get seriously overcharged, develop great heat & must be isolated as soon as possible. Generally this only affects the faulty battery.
Note also that new batteries are stored dry charged. i.e. they are fully charged after manufacture then all the electrolyte is drained out. This gives them a long shelf life in the dealers & allows for safer shipping
, but requires filling them with battery acid (not distilled water) before use. For this reason beware of any new batteries you may purchase
already filled with electrolyte. They start ageing as soon as that happens.