LiFePO4 Batteries

LiFePO4 vs. AGM

Plan A for our batteries were the Firefly International Energy AGMs (absorbed glass mat). Earlier this year we heard about a this newer technology for AGM batteries called Microcell which is a carbon foam.  Originally it was developed by Caterpillar, Inc. for their heavy machinery.  They sold the patent to Firefly International Energy who started manufacturing them in India.  Supposedly, they recover to full capacity after discharge and they operate in partial state of charge for days without loss of capacity which has always been a big downside to regular lead acid batteries.  Once regular lead acid batteries are discharged too low, some of the original capacity is lost forever.  The Fireflys have a longer cycle life and resistance to sulfation.  They are a little more expensive than a lot of other AGMs BUT they are a lot less expensive than lithium batteries.  They seemed like a great compromise between price and performance.

We called a local Firefly vendor and they said they only get them sporadically.  They had no idea when the next shipment would be.  And they didn’t have a waiting list we could put our names on. So we resigned ourselves to ordering them online and paying an arm and a leg for shipping.  But again, we couldn’t find anyone who had them available.

Then in April at the boat show in Richmond, Rich attended Nigel Calder’s boat electrical seminar.  Nigel was who we had originally heard about this great AGM technology so we were interested to hear what he had to say.  The bottom line is he said the technology is “a game-changer.”  However, since the manufacturing process was moved to India the quality of the batteries has suffered.

So on to Plan A version 2.0

For about 5 months we were planning to buy regular AGM batteries.  We just needed to figure out which brand and how big.  Our two big hangups with AGMs is that you only get about 50% useable amp hours and they weigh a lot.  So if you buy a 150 amp hour battery, you can plan to get 75 useable amp hours out of it before it needs to be charged.  The area for our batteries is SMALL, which means we have to cram as many amp hours into it as possible.  Neither of us were really happy with the choices of AGMs.  Plus, we had to consider the weight of the batteries since they are located on one side of the boat.

Fortuitously we dragged our heels on buying batteries.  I guess we were distracted by all the deck work we were doing this summer.  When fall came around we started shopping around for a Victron battery charger/inverter.  There are a few local (Bay Area) shops that sell them, but their online stores are non-existent and we avoid going to the Bay Area if we can help it.

Then I found a place in San Diego called Bay Marine Supply.  They had a great online store and they sold the Victron we wanted.  They had an electrical “kit” for sale with a few options to select from.  Rich called them up and spent over an hour on the phone talking to one of their technicians about what would work best for our boat.  They were SO helpful.

Plan B is born

They also sold a brand of LiFePO4 (lithium iron phosphate) battery I’d never heard of called Battle Born.  I looked them up and they’re in Reno, Nevada (relatively close to us).  The batteries are 100 amp hours each, weigh about 30 pounds and are the size of a Group 27 battery (a little smaller than the Firefly and smaller than other comparable lithium batteries).  The great thing about lithium batteries is that they can be discharged nearly all the way down without losing any capacity.  Of course that’s not the best way to manage the batteries, but in general they have more useable amp hours than AGMs. 

For example, with five 100 amp hour AGMs you can rely on about 250 amp hours before they need to be charged.  With five 100 amp hour LiFePO4s you can rely on closer to 400 amp hours before they need to be charged.  And the weight savings is huge.  The Firefly AGMs weighed 75 pounds each!  That’s 225 pounds more than five Battle Born LiFePO4 batteries.  That’s a big deal when all that weight is on one side of the boat.

Our original reason for not wanting lithium batteries was the cost.  The cheapest we’d found was around $1300 each or $6500 for 500 amp hours.  And we didn’t think we could even fit 5 of these batteries under the quarter berth.  The Battle Borns were $899 each which is about $400 more than the Firefly AGMs and $400 less than other lithiums.  Plus, they have a 3 year warranty, the technician at Bay Marine spoke highly of the Battle Borns and they’re made in the USA so that’s bonus.  If we do have a problem with any of them, we can drive them up to Reno if we have to.

Our second reason was the safety issue.  Lithium batteries can be prone to thermal runaway reactions.  On a sailboat that means your boat ends up at the bottom of the ocean.  Advances in lithium battery technology, such as using safer and less reactive cathode materials (e.g. lithium iron phosphate) has greatly improved the safety of the batteries.  On top of that, most LiFePO4 batteries have a battery management system (BMS) built into the battery.

All Battle Born Batteries use the safest and most stable components, including a LiFePO4 cathode and a built-in Battery Management System (BMS). The BMS protects the cells against excessively high or low voltages, high currents, short circuits, and excessive heat or cold. These are the most common causes of battery failures, and we have taken every precaution to mitigate these risks in all of our batteries. In addition, all of our cells are manufactured in a state-of-the-art automated facility, and each cell is cycled multiple times to ensure quality and consistency.

Li-ion batteries can actually be safer than Lead acid batteries, which have no protection against ground faults. Our batteries have a built-in BMS that protects against ground faults.

It didn’t take much to persuade Rich to consider the Battle Born LiFePO4 batteries.  There were too many upsides to consider.  The only real downside is the cost.  Plus, with the complete overhaul of our electrical system, it’s the best time to make the switch from lead-acid to lithium.  We had to buy all new equipment anyway so why not get stuff compatible with lithium batteries.

Installing Water Tanks
2017 Projects Recap


  1. That’s to bad about the Firefly batteries! They were on my short list to purchase when our lead acid batteries die. Oh well, technology is aways changing and our batteries should last several more years. Nice posting and good information!

    1. In a few years, they may have better QA/QC in their manufacturing process. Just in time for you to replace your batteries. I hope so because they sound great.

  2. But that’s still a pretty hefty premium over the cost of flooded cell batteries… I believe we paid about $900 for six Group 31 flooded cell batteries a few years back – for a total of 450 useable amp hours capacity.

    They are getting cheaper every year but I think you still need to have some special requirements (as you do: limited space, weight…) to justify the cost premium for lithium batteries

    s/v Eolian

Comments are closed.