For trickle charging and topping up lets say you want a 5amp possible charge current at 48 volts this is about 250 watts total of panels. 2.5 amps would be 125watts of panels. What size will your battery bank be in amphours at 48volts? Note a 100amphour 12V battery gives you 25amphrs at 48vlts. That is the place to start.
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