MrGiggles said:
Been considering it more and more, but for me they are just too expensive to justify at the moment. The weight is not a huge consequence in my boat, and the Everstart 29DCs I run now last a long time and are 1/5 of the price.
The way I see it, lithiums would need to last 20 years or longer for them to pencil out, being 5-8 times the cost of lead-acid.
The weight savings are certainly desirable in smaller boats, and you will get a little bit more capacity out of them.
Depends on how you use the batteries. For me, the initial outlay is big but in the long run would cost me a lot less money, which is why I am shopping for them now. I use my 36volt Ulterra to coldwater fish a lot different than most you guys that mostly warmwater or fish in the saltwater. I use it as an autopilot and speed control device in harmony with my gas kicker for thrust. Because of that, I tend to deep discharge my batteries almost every time I go fishing. Deep discharging wet cell batteries is very bad for them. I go through a set of 3 group 31 lead acid batteries in about 18 months because of how much I abuse them. I can run them longer than 18 months if I am willing to accept much shorter run times- which I don't. I generally buy Interstate batteries, they are $180 each. Doing the math on 10 years of Interstate batteries, replacing all 3 of them every 18 months or so is approximately $3600 worth of batteries over the course of 10 years.
The group 31, deep cycle, wet cells I use are rated for about 105 ah each. Wired in series for 36v I remain at 105ah approximately. So if I use that as a benchmark, the 100ah lithium batteries I see that are capable of being wired in series run about $899 each. The ones I've been looking at carry a 10 year warranty and are rated to 6000 charge cycles (way more than I'd use in 10 years and probably more like 20 years). So I'm looking at less than $2700 for 10 years of batteries.
There are some very appealing traits to lithium power other than just weight for a trolling motor especially:
-Lithium batteries do not suffer if they are deep discharged below 50%. So I can pretty much drain them and not worry about ruining them. They can also be charged or discharged partially without any negative performance or longevity. They are very forgiving to abuse.
-Lithium power is not the same as wet cell power. Not even AGM's are close to being equivalent in how much power they provide. This is hard to explain without getting really technical, but the fact is that 100ah of wet cell batteries is more equivalent to 60ah of lithium power. Your run times will be much longer with equivalent amp hour ratings between wet cell and lithium.
-Lithium batteries are digitally managed by a BMS (battery management system), and because of this the power is much more stable than wet cell power. The BMS is designed to deliver the same exact voltage 100% of the time it's in operation unlike wet cells. Wet cell batteries continually lose voltage until they finally reach zero voltage. Because of this BMS it's also possible to know exactly how much power has been used and is left to use. I would really like a 100% accurate battery gauge unlike wet cells where the resting voltage on the average meter can be deceiving. With lead acids you pretty much need a load testing battery meter, and even then it's not 100% accurate.
There are certainly some disadvantages, the most of which is initial cost, but doing the math it's FAR more economical using lithium power over the long haul. The other big disadvantage is that the BMS will instantly cut power when the available voltage range has been used, whereas a wet cell it would still deliver power, it would just be weak. They also can't be charged in the cold unless it's a certain kind of battery with an integral heater.
Anyway, that's the math I've done, and I'm now shopping for some lithium batteries.
