A boat’s engine-cranking and domestic batteries are on separate circuits so that the starting battery isn’t accidentally drained, but you need to be able to combine the power from both batteries to help start a reluctant engine. Usually this means installing either three single switches or a four-position (off, 1, 2, both) selector switch; either way, it’s all too easy to leave the switch in the wrong position. The Dual Circuit Plus battery switch from Blue Sea Systems removes that possibility. You just switch it to “on” and the engine will charge both batteries while loads will be taken only from the house battery. Switch over to “combine” if you need both batteries to crank the engine. Available in 200- and 300-ampere ratings, $34.53/$41.93. Blue Sea Systems; 360-738-8230; www.bluesea.com
