I have a 75 AH deep cycle battery(AGM) and I have a battery charger with 2 modes, 5.5A for car, 2A for motorcycle, as far as I remember, lower charging rate is usually better for longer battery life and better charging, my questions are if what I remember is even true, and if so, does long charging affects the battery? For example, maybe lower charging rate might be better, but if it takes very long to charge it makes it worse? Long story short, which mode should I use, the 5.5A or the 2A? Thanks :)
A widely recommended maximum charge rate for lead-acid batteries is about 20% of the Ah rating, so 15 Amps for your 75 Ah battery. So use the 5.5 Amp setting.