Upgrading the Batteries: Lithium Ion on a Sailboat

sailing luna sea cruising travel blog

Our boat has “some of the best” batteries.

Luna Sea came with two Lifeline 210amp hour batteries.  Don’t worry, we didn’t really know what that meant either.  Turns out that is a fantastic brand of AGM batteries.  They are much more forgiving to being over-used than typical boat batteries.  This results in a longer lifespan than less expensive batteries – so you may end up saving money in the long run.  The current batteries have done everything we’ve asked them to do, thus far.  But we’ve been at a dock for 3 years with unlimited shore power – so we haven’t asked them to do all that much, really. Multi-week trips we’ve taken lead us to believe that if our batteries are fully functional, they are sufficient in size to meet our needs.

We have no idea when the previous owners purchased the house bank, but I’m willing to bet it wasn’t right before they sold the boat… So our best guess is that they are somewhere between 4 and 6 years old.  That’s actually pretty remarkable for boat batteries, from what I hear (typical lifespan seems to be 3 or 4 years).

We didn’t know how to use our batteries properly, when we bought the boat.

As with everything we’ve done on this sailboat, there was a learning curve on how to properly use and care for our batteries.  The House Bank is a collection of one or more large (two 210ah 12v, in our case) batteries that run our daily devices: led lights, refrigerator/freezer, radio, radar, navigation equipment, water pump, water maker, fans, etc, etc.  The only things on this boat that require typical American 110 power are the air conditioner and the outlets.  We’ve already discussed that we won’t be using our a/c.  That leaves electronics that require 110 power.  We have 2 small inverters (and I mean SMALL) that we can plug our small gadgets in to charge – think Sonicare toothbrush charger, rechargeable hand held vacuum cleaner, hand held vhf radios, etc.  We also have 12v USB plugs in a few places on the boat, so we can plug in our phone/tablet/Kindles and so on.

Turns out traditional batteries only like to be discharged to 50%.  We did not know this until well over a year into boat ownership.  You don’t know what you don’t know…  This means we likely dropped our charge on our batteries well below the 50% mark, multiple times.  For example, if my battery charger reads 100% charged, and the fridge runs all day, it may drop down to 75% charged.  We presumed that meant we still had 75% of our power left.  Wrong.

Electricity/Battery Use has a steep learning curve for us.

Please to not read this and think I know what I’m talking about.  I am seriously learning as I go here.  But I want to share what I’ve learned.  Maybe you don’t know this either, and it will give you a jumping off point to start your own little adventure into the realm of electricity.

Here are some of the things I’ve learned so far:

⚓️ If you have traditional batteries and you charge them to 100%, you shouldn’t let that power load drop below 50%.  Ideally you don’t even drop that low.

⚓️ Most batteries need some sort of maintenance.  The Lifelines typically need to be “balanced” once a year.  This means you need to give them a higher than normal charge for a few hours.  They normally charge around 13.8 volts or something, and need somewhere in the 15 v range.  Again – do not take this as hard data.  Do your own research for your own set up.

⚓️ We have solar panels that charge our batteries.  One of our projects last year was to upgrade our solar.  There was some sort of misinterpretation of data and we thought we could use the solar controller that was already on the boat.  We cannot.  We have overpowered our solar controller and need to upgrade.  Immediately.

⚓️ Lifelines are particularly forgiving to being somewhat abused, but they are not magic.  They have aged AND taken a beating.  When our fridge started having issues kicking on, we knew we had to act.

⚓️ Running your engine allows your alternator to charge the batteries.  If the batteries are shot and won’t hold a charge, the alternator works at top levels non-stop.  Guess what this means?!  I just had our alternator rebuilt this week.  Thankfully we sailed our way back to the marina when we realized we were having trouble, and it prevented us from doing significant damage/needing an all new alternator.

We knew when we were planning our first month off the dock that our house batteries were questionable…

I felt like our batteries were beginning to struggle.  There weren’t really many power drawing additions – in fact, we more than doubled our solar capacity, so why couldn’t the batteries keep up anymore? After digging around on the internet and through our maintenance manuals, I learned that we needed to completely unplug our batteries and let them “rest” and then we could test them.  The amount of time recommended for resting the batteries before checking them with a meter varied depending on the source, but the bottom line is that we live on this boat full time and having no power whatsoever was not really an option.

We decided to wait on our decision until we left the dock and were living fully on the batteries – no shore power back up to charge them, just solar and engine (when we were motoring).  We also have a small portable generator, just in case. Because we can’t go south of Brunswick until Nov 1st anyway, we figured we could just call our first month out our shake down cruise.  We are in our home waters and can get help/order parts fairly easily from here.  Friends are all around and several of them have power boats, so if we really needed it, someone could come out to us at anchor.

We headed into Hurricane Matthew with crappy batteries.

We left the dock knowing that our batteries were questionable, and that a hurricane was barreling toward us.  But hurricanes always turn to the east when they are projected to come here, and maybe our batteries weren’t actually bad anyway.  We were in La-La land on both accounts. Let’s just say that the stress of prepping the boat for the storm while simultaneously realizing we had serious power issues clarified our need to order new batteries.  No one wants to be the Power Police, but we both were constantly checking battery levels, which lights were on, etc.  We were stuck in four days of rain and couldn’t even binge on Netflix for crying out loud.  Clearly we had to pull the trigger.

Waiting on the price drop.

Mark has been researching alternative battery sources for about a year.  He landed on LiFePo4 – a lithium ion chemistry that is showing remarkable results.  The batteries are a fraction of the weight of our AGM batteries (75lb total vs 248lbs).  You can practically drain the batteries completely without damaging them.  They charge significantly faster – which means as we use them during the day, there’s still time for the solar panels to top them off. The downside?  The price.

Replacing 2 Lifeline batteries costs about $1600 for a direct replacement.  That means two 210ah batteries.  But remembering that we can only use them to 50% means that we would have 210 usable amp hours.  Bonus crappy fact: they are only able to produce their full amount of amp hours for a fraction of their lifespan.  The older they get, the less they are capable of producing.  And they take 30%+ more time to recharge.

Replacing our Lifelines with three 75ah Relion Lithium Ion batteries costs about $2992.  That is 225ah total.  And pretty much all of that is usable – and should recharge much faster.  But here is the real kicker:  Lifeline batteries have a lifespan of about 300 cycles.  They also have a 5 year warranty.  The Relion batteries have a lifespan of thousands of cycles.  Yes, thousands.  And they have a 5 year warranty.

While we were naively hoping our batteries could last another year or so, in the hopes of a significant price drop, that is not happening.  We have to buy the batteries and we have to do it NOW.  We can’t run the engine until we have good batteries – or we’ll end up needing to replace that alternator.  And if we can’t run the engine, we can’t leave the dock.  And the Bahamas are calling.

I pulled the trigger.

After researching a few different brands, and getting a first hand recommendation from another cruiser for Relion, I pulled the trigger and bought the expensive-as-all-get-out LiFePo’s.  I spoke with a sales rep and he was very patient and explained things thoroughly.  He helped me figure out what solar charger we actually need (25a MPPT) and how to get the most amp hours into the space we have available.  Two 75ah LiFePo’s will fit in the space of one of our 210ah AGM batteries.  I ordered 3.  We think 225 ah will be enough, but if not, we still have space for one more.  As long as we add it relatively soon (say, the next 6 months) it won’t be a problem to purchase it later.  You know, when the current sticker shock wears off…

So I’m saving money how?

In no way shape or form am I happy to be spending this much money (although I AM thankful that we have stashed away money to do exactly these sorts of projects).  BUT. In the grand scheme, if these batteries live up to the hype, this purchase will actually save us money in the long run.  They have a 10 year or so lifespan vs 3 to 5.  Keep in mind, a direct replacement would have cost me $1600 now and then that much, if not more due to price changes, in 3 to 5 more years.  I could potentially have to replace them now AND at least 2 more times in the theoretical lifespan of the Relion batteries.  That makes the $2992 price tag a little more palatable.

Only time will tell.

Fingers are crossed that the batteries arrive today and we can begin the task of installing them.  The new controller will arrive next week.  Once they are all installed, it will just become a waiting game to see if this purchase was the right choice.  As with our other alternative choices (CopperCoat bottom paint, hard top, TuffCoat deck paint) I feel like we are making the correct, low maintenance choice for our boat.

While we wait on the stuff to arrive, we have to take the puppies to get their booster shots for some of the vaccines they needed to get into the Bahamas.  Sure, we’d love to be out on anchor right now, vs at the dock.  However, we are so grateful to have this home base to station ourselves and take care of this major project.  I am happily looking forward to getting this all straightened out and untying those dock lines!  Again.

PS: No.  These batteries are not going to burn down the boat.

There is a lot of talk of lithium ion batteries causing fires.  As with all things, there is a grain of truth here.  At one point, the aerospace industry was using a type of lithium ion batteries.  They were catching on fire.  (Think Samsung Note 7’s – but I have no idea what chemistry those use) That is not cool.  But this is different chemistry.  The newer version is much safer and not burning down peoples boats/homes/planes.

I will likely do another post on the install as well as a follow up.  Do you have any first hand experience with the current LiFePo chemistry batteries?  Are you looking into it? Already have it?  I know we are not the only people watching this technology!


  • Mark and Cindy - sv Cream Puff


    Very cool. Did you also have to replace the shore power battery charger? And, how does the engine alternator work with the new battery charging requirements?

    • Jennifer

      Hi Cream Puff crew! Fortunately the existing shore power charger and alternator should both be compatible. As of right now, the only additional purchase is a third cable to go from two batteries to three. But it IS a boat project, so we will see!

  • Chris French


    We upgraded to Lithium batteries this year and have a number of blog posts on the subject. Check them out if you are interested in our experience: http://www.svstrikhedonia.com/super-charging-the-power-systems-lithium-battery-upgrade-installation/

    • Jennifer

      Thanks Chris! I will check out your site. Thanks for chiming in!

  • Bill


    Helpful article for planning a cruising power plan!

    • Jennifer

      Thanks! Trying to share as we learn. And we are still learning on this one!

  • Glenn


    Do you have electric primary winches?
    I found current draw is quite high using such with lithium batteries.
    The BMS on battery drops the batteries out

    • jennieprince@hotmail.com

      No, Glenn. We are fairly low tech in most regards. Manual winches, manual toilets, minimal exterior wood. Salt water corrodes everything. Oh, and we are lazy. Our windless and water maker both have high draws, but the batteries easily recharge from their use.

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