My observations and considerations, in no particular order:
There are a couple of "Lithium" technologies out there: Lithium Ion and Lithium Iron Phosphate (LiFePo). The LiFePo batteries were the ones that came out maybe ten years ago? Everyone thought they were awesome, never die, weigh nothing, etc, etc. If they had delivered all these promises, I'd have expected everyone to adopt them. Instead what we've seen is few bought them, the ones out there have their own issues and they've never really caught on.
One of the issues with LiFePo batteries is that they don't have full output when they're cold. I forget the numbers but, I believe the cranking amps start dropping off below 50 degrees. Nothing like coming out of brisk hotel morning to your bike in 35 degree weather and not being able to start it. You can turn on the lights and let them run for a few minutes. This allegedly 'warms up' the battery and then it will start. I don't know since I haven't had one.
I got a thrown away LiFePo battery I found in a recycling bin. I took it home to disassemble and see what's inside. I was amazed to find regular D-sized cells, soldered together to make a 12-13V bank. It includes a charge manager board that absorbs the excess going to each cell. What that's needed for is balancing the cells and not overcharging any one cell which would permanently damage the battery. What had failed in that battery was not the cells but, that charge manager. So while the battery part should have this claimed long-life, the stupid charge manager board didn't. That ended up damaging some of the cells, which killed the whole thing.
So LiFePo technology was kind of out. What about Lithium Ion batteries? Well, they are very particular about how they're charged and if you overcharge them, they catch fire. We've all seen the news stories of electric bicycles catching fire inside peoples garages and apartments. The last thing I want is a fire source like that on any of my bikes. This is aside from the fact that our Lithium Ion batteries in our phones rarely last more than 3-4 years.
Its so bad that I have an old iPhone that I use for music in the garage. The battery is toast but, I don't dare leave that thing plugged into the charger except when I'm listening to it. It gets unplugged and the battery is dead literally overnight. I've read that Lithium Ion does best when always used between 20 and 80%. Fully charging and fully discharging them damages them.
Given all the negatives with the competing technologies, I stick to regular Absorbed Glass Mat (AGM) batteries for now.
