Two years ago I did a lot of research into Lithium Deep cycle marine batteries. I wanted to know all I could about them, and find the best and most affordable brand(s). Not nearly enough room here to tell you all that I learned.

Miller Tech in Middlefield, Ohio. You can't beat them.
Home - Millertech

Great customer service and their batteries are actually real grade "A" batteries. I talked with them, and went to their facility to see their operation. They taught me a lot, including showing me a battery with the case removed, and how it's important how the individual cells are connected. If I remember correctly, you want a battery that uses bolts to join the cells, not welds. Welds can come loose over time through vibration and use. There are also other design factors and the type of cells that are used. I also talked with several other people who are in the business and knew a lot about these batteries.

All these Lithium batteries are made in China. The few companies here in the USA that make them are about double the cost. It's very important to have your batteries made by a reputable Chinese company, and consistently do quality inspections to insure your specs are being met. Miller Tech does that.

There are a lot of companies selling these batteries. Some are reputable, many are not. Beware any Lithium battery that is significantly less expensive than other brands. They are not nearly as good quality. It is so true with Lithium batteries that "you get what your pay for", meaning the less expensive batteries are almost never the same quality as the more (and not that much more) expensive brands. The less expensive ones work, and can last nearly as long as the more expensive ones, but you take the chance of an early malfunction and poor customer service if you need it. If you really want a long lasting quality Lithium marine battery, get a reputable brand at the (sometimes slightly) higher cost.

Also, as with anything, you need to take proper care of these batteries. The higher quality brands are fairly tough, since they are made for marine conditions. But abuse can lead to early wear out, and damage. If you follow the recommended use and maintenance, these batteries can last 15+ years or longer, depending on the amount of yearly use and how you treat them, as well as the conditions they are used in. Plus you get a much longer charge out of them compared to a lead acid battery, and they are a lot lighter in weight.

WB