Dual batteries off a switch

[Wrestling Coach]

I recently purchased a boat that the previous owner has set up with a dual battery system off a switch. Both batteries are marine batteries. Boat has electric downriggers, paper graph and fish finder/depth sounder. One battery is a marine cranking/starting battery but the other is a deep cycle marine battery. Any reason why they should be different? My question is the deep cycle. Two batteries are nice but can't I just have two cranking batteries?

[MCF]

Cranking battery will work fine-as described you have nothing which is a significant drain like an electric motor.

[jimski2]

There are different charging voltages for those different batteries, but they work. The battery switch must be checked to see if it has a alternator disconect switch inside it as you can blow your diodes on the boats alternator if you switch the batterys when the engine is running. They make different types of battery switches so be careful. Starting your engine on the deep cycle side only can harm that battery also.

[Wrestling Coach]

This boat is an older Grady White Tournament 190 IO 470 motor. I have a second boat, a Lund, with an outboard. It also has two batteries, 1 cranking and 1 deep cycle for the bow mount trolling moter. Whenever I run the deep cycle down I charge it from a 110v charger in the garage and then on a maintainer after that. I have never had a boat that would charge both batteries on board not to mention a deep cycle. So just trying to sort things out here so I can do the right thing when the time comes to get some new batteries. Thanks for your input and advice.