Add a lithium battery in series w/ lead cell?

I am looking into adding lithium batteries to my boat. I am looking primarily to shed weight. I currently have a 36 v trolling motor with 3 interstates and 1 starting battery. This is considerable weight to my old Gambler. I have researched on the web and have asked many people but keep getting conflicting information. I understand the lithium requires a separate charging system. My question is can I add a single 12 v lithium battery in series with my other lead cell ones as they go bad until I eventually have all lithiums? I have had reputable service dealers here on Lake Fork tell me I can. While at the same time I’ve had others tell me not a good idea…but without any specific reasoning. If I could afford to replace all of them at the same time I would but I am on a limited budget.
Can we discuss this without causing a riot?

Edit: my full charge voltages are probably not accurate, but they are what I see in my batteries and the example/situation is still the same.


The lithium’s hold charge at a much higher voltage. They are fully charged around 14.1v (might be 14.3, but give or take a smidge). Regular lead acids are fully charged around 12.6v (give or take a smidge). What happens if you add a lithium to the lead acid, is the higher voltage lithium will be constantly sending voltage to the lead acids. Basically, you’ll drain the lithium, but keep the lead acids charged more, due to the “battery balancing voltage” amongst the batteries.

For a day or two, not a big deal. Don’t want to do it long term though. If you want to unhook the lithium from the series, when the boats sitting and not being used, you could do that. Potential fire danger with the loose wires hanging around, but you’re a fireman, so I think you got that covered.

Now if you had an agm, which carries a higher voltage than a lead acid, you could do what you are asking. No weight saving with an AGM though and you don’t have those anyway. That was more for anyone else reading this.

There is a reason why salesman tell you stuff….to sell stuff…

No!

The best advice I can give is contact the lithium battery factory of the brand you are considering and ask them. You will get many I THINK answers here.
Go to the factory web site and contact them.

THIS!

They don’t speak English in china.

Give Jones Trolling Motor in Texarkana a call. They can steer you in the right direction.

Different animals with different voltage curves as they are used. Also, they need a different type of charger unless you have something like a Noco charger. Take a look at the 100ah EG4 batteries, reasonably priced (@550$ each) with 5 yr warranty. But nothing like the quality, customer base, and app which you will get with Ionic. If you fish allot, you will be very very surprised going to lithium. I removed 2x Wally world deep cycles at 75lbs each and replaced them with two 22lb 100ah EG4 batteries and I can go two (long) days with the ultrex 24v on a 18'6" older champion.

But don't mix the lithium, that's a insurance deductible waiting to happen. It can be done, but I wouldn't do it. But if you do your research, you might find a way to do it safely. They both like a different charge. Lithium is best kept not at 100%, and you charge right before you use them. Wet like to be at 100%, so you have to charge them at different times to get the full life out of them. I have my lithium charger on a smart device that I can turn on before I go fishing, and I can turn it off remotely.

Good luck, and let us know how it all turns out. My good friend had a Gambler, absolutely the most amazing ride in rough water to date. 25+ winds, 65mph riding the tops of the waves.. truly amazing.. I'm a little Jelly to be honest..

Prosise