All Grady-White boats 20 feet and up have at least two batteries, connected through a battery switch. However, the switch is not as simple as turning it to the “Both” position and heading out.
When you leave the switch on “Both”, you are, in effect, fooling the engine’s charging system. If one battery is weak it will not be getting recharged because the motor thinks the voltage is OK.
The only time you want to be in “Both” is if both batteries are so weak that neither one will start the motor by itself. Switching to “Both” will combine what power is left in the batteries and that may be enough to get started.
The ideal way to use the switch, and get the longest life out of your batteries, is to use battery #1 one day and battery #2 the next time you go out.
There is one more cardinal rule and that is “Never turn the battery switch to off with the motor running”. That will result in instant damage to the charging system.
And, unless your boat has something that requires 12 volt power when you are not on the boat (refrigerator, for example) turn the switch off. In that way, the battery will not be run down if you accidentally left something turned on.
Remember, on a Grady the bilge pump and electronics memory wires bypass the battery switch and go directly to the battery so they function even when the switch is off.