said by kf6ytc 
:High end batteries will have a charge voltage, ie. 12.9 volts....... If you get a good power supply, $50 for a switching one, about 10amps, just adjust the power supply to the charge voltage (12.9) and the powersupply will charge the battery, but once the voltage of the battery is also 12.9 the battery will draw virtually no current from the supply, so you can leave the power supply on the batteries without having to turn it off, or overcharging.
The float voltage depends on the battery construction AND on temperature. A long life charger must be temperature compensated.
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