View Full Version : Battery Types?

Patrick Hardy
06-25-2009, 11:25 AM
After reading Diesel's extensive dual battery thread and the battery power thread, multiple people mentioned that you should be using the same type of batteries for your boat. My question is when they say the same type, do they mean flooded or wet cell, gel, agm batteries? or do they mean using only starting / cranking vs. deep cycle batteries? I thought that you should use the starting battery to start and a deep cycle to power everything else? Thanks for any thoughts.

06-25-2009, 12:11 PM
Here is my understanding:

I would always use all of the same type battery because your alternator only sees one large battery when they are combined and being charged. If you have even small variations in the charges of your batteries, the power output from the alternator is going to 'forcefeed' the battery with the lower charge. When the batteries are combined they will also discharge from one battery to the other until a steady state is achieved. To minimize that, I always use all of the same battery.

I know of plenty of people that have used a starting and deep cycle together, and have not had a problem. So I don't think it is a major issue. I can say for sure that the stereo installers on Wakeworld pretty much always use the same batteries for everything. Electrical gremlins can be so tough to sort out that it makes sense to me to decrease the odds that the battery differences are a source of issues.

DEFINITELY, do NOT mix lead acid and AGM batteries. They have very different charge and discharge rates and you will ruin one of them, usually the AGM because they cannot accept a charge at the same rate that the lead acid battery can.

06-25-2009, 01:01 PM

06-25-2009, 03:20 PM
That helps a lot. Thanks for the info.

06-25-2009, 04:31 PM
On testing my batterie can I just buy a battery tester from an auto parts store or should I pull them and take them in?