The simplest is to get a manual not phart charger rated as close to 5% of total amp hour rating of your total battery or bank amp hour capacity and let the charger charge until voltage raises to 15.0 volts. A SIX AMP manual charger is close enough for a single 6 cell RV battery.
If your panel IS CONTROLLER -LESS then you cannot bypass the controller and allow the voltage to rise beyond 14.0 volts. Otherwise, WITH A CONTROLLER, disconnect the wire leading out of the controller that goes to the batteries. Reconnect it directly to the wire coming from the panel. Beware of forgetting it and boiling the battery. Disconnect the charge when voltage reaches 15.0 volts.
HOWEVER too slow a charge rate can damage the battery if bit by bit day by day voltage raises to 15.0 Get the amperage around 5 amps not 2-3 at the start of top charging. The process is a formula.
Battery store owners LOVE people who insist plug and play smart chargers are the only way to go and "people who exert an effort to please the battery are wasting their time". This is why the subject appears to be controversial.
I simply do not have the money or resources to pay for plug n play mentality. I also use my batteries heavily and do not pontificate on the subject after using batteries two weeks per year off-grid.
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