When we purchased Odyssey I was very excited about the three large AGM (Advanced Glass Matt) marine batteries (380 Ah total) that had been installed for the house bank. With 190 Ah of useable energy (You should only discharge an AGM down to 50% of rated capacity) I dreamt of weeks on anchor, basking in all the electricity I could ever want. This has worked well for us.
- Lithium batteries are safe. (No matter what you have been told, they don’t catch fire and melt down like Chernobyl.) (At least, not anymore.)
- Lithium batteries have a much higher energy density. That means lots of power in a small, light package, at approximately 1/6th the weight and size of an equivalent AGM.
- Lithium batteries last a long time. Most are rated for ~5000 charge cycles. That's about 10 times greater than an AGM.
So over the life of the battery, lithiums cost a lot less (per Ah) than an AGM. You can save even more if you build the lithium battery pack yourself, which is what I’m going to do.