Battery Replacement

Well, this has been a long time coming, Our Lead Acid batteries were on their way out when we arrived in St Lucia, they had come to the end of their useful life (5 years) and it was slowly getting harder and harder to get them to hold their charge. The journey across and the issues that we had with the generator finally took their toll and we knew once we hit the States they were going to need replacing.

So what were the options to replace them with?  We could have replaced them “like for like” for traditional lorry type heavy-duty lead acid (Flooded wet cell), we could have gone down the popular route of AGM or Gel (VRLA), or we could really push the boat out (excuse the pun) and fit Lithium Ion Phosphate or LiFePO4 as they are more commonly known.


There has been a lot of controversy surrounding the use of LiFePO4 in boats, mostly coming from the mis-association with Lithium Ion phone batteries, which are a completely different beast and still from time to time have an issue with getting really hot as they charge or discharge.  The much larger marine modules have a built-in BMS (battery management system) that prevents the over or under charging, overheating and completely flattening the cell associated with the smaller Lithiums.

So why lithium?

  • Well compared to to the LiFePO4s, the Wet-cell, AGM and Gel (forerunners) all suffer from the climate and typically don’t perform or last as well as Lithiums in the Caribbean heat.
  • Because of the technology a typical forerunner capacity of say 500ah limits you to only using 50% of the capacity so of that 500ah you can only use 250ah before you start to damage the battery and shorten its life, LiFePO4s can literally be fully discharged (well at least 90%).
  • Life span or length of use on any battery is measured in cycles (how many times it can be discharged and then charged) other batteries normally top out at 400-500 cycles, whereas a LiFePO4 has 5000-10000 cycles, (obviously, both of these are dependent on use and maintenance)
  • Talking of maintenance, the others require tinkering, particularly the wet cells need their fluids checking, these and the others (VRLA) although sealed, still require ventilation as they all gas from time to time, LiFePO4s don’t gas and apart from the odd glance at the battery monitor do not require any maintenance.
  • Charging the LiFePO4s is also much quicker, even though we and many cruisers now have large banks of solar panels on the backs of their boats unless you’re really frugal, from time to time you’re still going to have to run the generator or engine to top them up. LiFePO4s charge in half the time so this means you don’t have to run either for as long and either annoy the neighbours or use that precious diesel.

So why doesn’t everybody swap out straight away?

In short, the cost! Not the overall long term costs, from the above I think it’s easy to see that long term they are actually cheaper (fewer batteries required, longer lasting etc) but the outlay the typical cost of the LiFePO4 battery compared to the forerunners can be 2-3 times the price! To us, it makes sense because we’re likely to be going to be doing this for a while and in warm climates, if you’re a weekend/4 weeks a year sailor then it’s going to be difficult to justify.

We went down the RELiON route in the end, we had backed and forth between RELiON and Battleborn batteries both very good batteries and not a lot between them in both performance and price, the deciding factor, in the end, was only their size, battle born at present only make a 100ah battery which meant that if we wanted to maintain our current amp-hour setup we would have to install 10 x 100ah batteries and additional cable terminations etc, whereas RELiON make a 300ah battery that was the same size as the existing wet cells, so apart from a minor alteration to some woodwork, virtually a straight swap.

As for the existing methods of charging, the Victron Quattro had a lithium Battery Setting as did both the solar MMPTs, the Balmar Alternator has an external regulator that also can be programmed for LiFePO4s the only thing we haven’t tackled yet is the Marlec wind chargers, but something to consider is that although its nice to have the facility to charge the batteries with the right settings, and using these settings will ensure you get the most out of your new investment, as previously mentioned, nearly all LiFePO4 batteries now come with a built-in BMS, so you can run them on your existing setup without making any alterations at all to your settings!





  1. I know a lot more about batteries now than I did before I read this but if you’d asked what I thought you’d do I would have said “buy the most expensive” which you have done. But I enjoyed the justifications very much

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