The Lithium fanboys have spoken, now it's my turn
Your last set of gels lasted for
15 years. That is pretty typical for a well care for set of gels, and unless you greatly change the way you use your
boat, you should expect the same life span out of a new set. For all those people who are telling you "Li are going to be cheaper---in the long run." How EXACTLY "long" is that going to be before he recoups the added upfront cost of a new Li install?
I think it is also kind of
funny that people can make a recommendation like "Switch to Li!" and not ask you ONE
single question about how you use your boat. I am pretty sure than any thoughtful Li fan would admit that they do not make economic or even technical sense for every person on every boat. I am making the assumption that the Gels you have had for a decade and a half have worked for you, and given you the energy you need when you need it. If that is NOT always true, THEN you should consider changing to Li, maybe.
The gels are going to be easier and cheaper to install than a new system of Li. You would see NO financial benefit (if ever) from Li until it was time to replace this next set of gels. And in the year 2038 when it is time to replace your new gels, NONE of us know what
battery technology will look like. But I'll bet you it will be better than the best you can get from Li today...
Installing a new Li system also cares a small--but real--technical risk. You, and your installed
equipment, are obviously well suited to your existing
batteries giving them a long and happy life. Upgrading to Li batteries cares a risk that things might not go well. Certainly there have been several people on here who have cooked an expensive set of new Li's through mismanagement of their systems. That will surely kill ANY imagined cost benefit for Li. The technical risk of replacing your batteries in-kind is very small.
This is NOT a technical criticism of Li battery systems. In the right application, on the right
boats, used the right way, they are really awesome. If you have technical needs for the benefits that Li bring, they can be obviously worth the capital cost up front.
This is just pointing out that the simple cost per amp-hour of a
project over a 30+ year life span is not really a very sophisticated economic analysis and doesn't address the real financial world.
In short, if the Gel batteries reliably supply
power in a way that works for the way YOU use your boat, I would stick with them. You will not get any extra "cool" points, but you will have a good chunk of extra
money in your pocket for the next 15 years, and that is not peanuts.