Lithium Battery For Starting and Trolling Motor?

I cannot find a definitive answer, just that deep cycle batteries are not built for crank batteries. Of course.

I have a 15' Boston Whaler, 60 HP Merc, 55# Minn Kota on the bow. Currently I have two batteries, even though the Whaler stock supplies only one. and they run the running lights from that one too. One battery is strictly for cranking the Merc. Unlike my previous experiences with Mercs, this 60 is bombproof. I can let it sit for weeks and it will fire up in maybe 1.5 seconds, tops.

The other battery is for everything else, including the trolling motor and the electronics. I can go a full day on the Delta with nearly continuous trolling motor use and be down to 60% at the end of the day.

Both batteries are AMG, 100 AH each.

The weight under the side console is enough that combined with a starboard bow trolling motor mount the boat can list to starboard a bit on a run when I am solo. My thought was to replace the two batteries with one, cutting the weight by more than the entire weight of the trolling motor. I would get 100 amp hours in this case which I guess would approximate the 200 AHs I have now with two batteries.

Any experience based opinions? Thanks so much!

JOhn

Apparently Mercury Marine specifically states that LI batteries of any kind should NOT be used with my outboard, and most other Mercs under 100 HP.To their credit, Dakota Batteries alerted me of this. If I stuck with AGM for the crank battery and went with Li for the electronics then I'd have no redundancy--not that I would with a dual purpose battery of any kind, but it sure would be great to replace 70 lbs. with 17 lbs.

John,

We have a 1979 15' Whaler as well with the original 75 HP Evinrude (runs like a top). My son built a platform to make it more casting friendly and provide some storage however this added weight (mainly plywood construction) so we have been looking into the lithium option as you are. Is the issue with using the lithium battery for cranking specific to the Merc or is this a general rule? We actually have three lead core batteries (one cranking, two for 24V trolling motor) which we have placed towards the center of the boat but the weight is noticeable.

I have reviewed different battery options but not within the last year so if you have any current intel on the options out there I am all ears.

Thank You
Jack