Electronics

GLENN HAYES is a marine writer and photographer whose background in the marine industry and in marine electronics spans almost three decades and many thousands of miles at sea traveling the world. He can be reached at

With demanding electronics and electrical systems onboard today’s boats, getting more power and efficiency out of boat’s batteries can be a challenge. One possible solution for some is the switch to lithium batteries.

Myth busters Before considering lithium batteries, some myths and misconceptions must be addressed. First, it’s important to know that the lithium batteries you find on boats are not the same type of lithium batteries you find in computers and power tools. Those are a specific kind of lithium-ion battery and are extremely flammable when the internals are exposed to the elements. Marine batteries are now mostly lithium iron phosphate (LiFePO4) and do not combust like certain lithium-ion batteries.

While it’s true that early lithium batteries aboard vessels got a bad reputation for possibly overheating and causing damage to electrical systems, chargers and even engine issues, this is not necessarily the case anymore. While some of those troublesome batteries are still out there, marine lithium batteries have come a long way in just the last couple of years.

Advantages There are some major advantages to choosing LiFePO4 batteries over other battery systems, such as wet cell and absorbent glass mat (AGM) batteries. The first is weight. These lithium batteries can be up to a third less in weight to a comparable wet cell or AGM battery. For example, an average group 31 AGM battery weighs in at around 55 to 60 pounds, while a comparable LiFePO4 battery with similar amp hours is about 25 pounds. With that much weight difference, you can really lighten a boat’s load. This, in turn, can improve ride, efficiency and performance.

Marine lithium batteries also have more energy density for a given weight. Some will say that it can be as much as a 4 to 1 ratio, while others have found it to be more like 2:1. With that increase in energy density, you can also experience space savings.

LiFePO4 batteries also have a notable cycle count. Most can handle up to 2,000 cycles compared to about 200 for a lead acid battery. This can be a huge advantage if the battery is used a lot and is run down frequently. Not only are these batteries capable of charging full cycles more frequently, but they also have more of that power readily usable. A LiFePO4 can offer up to 80% of its available amp hours of power to be used, while an AGM and wet cell realistically can offer much less (as low as 30-50%). LiFePO4 batteries also output 13.4-12.8 volts through their entire power output unlike a traditional battery where the voltage drops as output continues over time. They also self-drain at a slower rate than traditional batteries when idle and not being charged.

Downsides With all these benefits you may ask yourself, “Why not go with lithium batteries?” There are a few good reasons, the first being cost. You may get sticker shock when you first see the price of a quality lithium marine battery. The better and, as a result, more expensive lithium batteries will have a battery management system (BMS) that will control output and regulate temperature and power, ensuring it doesn’t overload charging systems and engines while still outputting power. It’s also important to make sure the battery you purchase is set up to be a starting battery if that is going to be its primary purpose. Buying a lithium that is not programmed to be used as a starting battery can shorten the life of the battery and introduce your boat to electrical issues. Some outboard manufacturers will not warranty their engines if a lithium battery is used as a starter.

Another important consideration when thinking of switching to lithium is to make sure your charging system is capable of handling lithium batteries. Many are not and will need to be replaced if making the switch.

While the cost of lithium can be high, the long-term cost can be equal or even less than replacing wet cells or AGMs over time. Some lithium battery manufacturers offer five-, 10-, even 11-year replacement warranties, and the cost savings over time can be significant. It’s important to remember, though, that the added cost of lithium is most justifiable if the batteries are used a lot and cycled often. If you’re not taking advantage of the added cycle rate, and the other advantages like weight and energy density aren’t important, the added cost may not be justifiable. If you are an occasional user and don’t work your batteries hard, then lithium may not be for you. ★