Most of us cruisers have probably either made the transition to lithium batteries, or are wondering whether we should. And, at first glance, what with all the claims and counterclaims made by each side of the debate, this seems like a horribly complex decision.
The lithium fan-boys, often in the grips of confirmation bias, scream "no brainer", while the reactionary lead-acid stick-in-the-muds yell "unreliable and will probably burn your boat".
Both positions are wrong.
But, not to worry, the decision becomes easy as soon as we cut through the claims to an understanding of the fundamental difference between the two chemistries.
And, further, once we have that fundamental locked into our heads, it becomes easy to select the right system for us and our boat.
What's that fundamental?
Lithium batteries store about four times as much usable energy for a given weight and volume as lead-acid batteries do.
Yes, I know, four times seems high given that a good-quality lithium battery weighs about 40% of a lead-acid battery, but the difference is that lithiums can be consistently cycled through about 80 percent of their range and lead-acid about half that.
Lead-acid salespeople claim 50%, but 40% is more realistic in typical yacht use due to tail off in charge current, making full charge every cycle unlikely, although solar does help with that.
And, yes, the savings in weight of lithium tends to be more than the savings in volume.
So let's just stipulate (as the lawyers say) that four times is a rough approximation. Don't worry about it...for our purposes it will do. Remember, this article is about a simple way to decide which batteries to buy, not an challenge to get into a mind-numbing debate about every detail.
If you are a lithium-lover and want to use five, or a lead-luster who wants to use three for the factor, that's just fine with me; besides, it will make little difference to the final logical outcome.
OK, so now we know this basic difference between the two battery types, the decision comes down to two questions each of us need to answer for ourselves: