svaeolus avatar image
svaeolus asked

Best practices to maximize LIFEPO4 useful life?

I'm in the final design stage of an all-Victron LIFEPO4 upgrade for my sailboat. MultiPlus, 2 of the LFPSmart 12,8/200-a batteries, VE Bus BMS, BMV-712, battery protect, cyrix, Victron MPPT solar controller, new Balmar alternator regulator and Sterling APD...the works, very similar to the example system diagrams Victron provides. Given the amount this is going to cost, I'm keenly interested in designing the system for maximum utility AND maximum useful life. I'd like my children to inherit this LFP system :)

My typical usage pattern is to not really need the house bank most of the year, but for 4 - 6 weeks in the summer my family pretty much lives on the boat. So we see a period of intense use in the summer, but the rest of the year I would like to do what I can to keep the LIFEPO4 batteries in a "storage mode" if that will prolong their life.

My understanding is that when not in use for a while, they should be stored in a partially depleted state...60%, 70%, 80%, I've seen figures in those ranges, with the BMS and all other loads disconnected. I figured I could manage this, running my minor house loads at the dock (bilge pump, never really runs, lights and radio when I am at the boat in the winter working on projects) off the AGM starter battery, which has its own 10amp dedicated shore power charger (not the MultiPlus)

But I've also read in the Victron battery manual that they should be fully charged once per month to keep the cells balanced, which seems to defeat much of the point of having a system in place to store them in isolation at 75%-ish charge for extended periods of time.

What are your thoughts on habits and system design for maximizing LFP battery life?

Is it a false economy to try to maximize life by being fussy managing the storage charge level, disconnecting and reconnecting the BMS and then diligently charging to 100% every month? Is it better to just "set it and forget it" and keep the MultiPlus going all year long? I want to avoid trying to be too clever and cutting off my nose to spite my face, if it is not really worth it.

Part of my concern here is "what counts as a cycle" when we talk about things like 3000 or 5000 charge cycles as being the useful life of a LFP battery. I hate to think I am using up my precious finite lifetime charge cycles just bouncing up and down between 95% and 100% at the dock while getting zero utility from the system.

Lithium Battery
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2 Answers
Jason Bolduc avatar image
Jason Bolduc answered ·

I believe you've already done quite a bit of research about the best ways to extend the life of LiFePo4. Much of the initial information I found still is tainted with information based on lead-acid chemistry, and of course LiPo which is a different beast again.

LiFePo4 does not have a real preference from 30% to say 90% for "storage mode" most sources says store them at 50% charge. I have not read of any significant damage occurring when other SoC's are stored. It comes to personal preference then I would say - with a conservative view being "store them at 50%".

This article provides a good balance of information: ( )

Regarding cell balancing, I would follow the instructions given by Victron for the battery pack you bought. There are different ways to keep a battery pack balanced and it does matter if you follow their recommendations.

As you already understand the danger of "parasite" loads when they are not in use, you have that covered.

I expect with such a setup you have a remote console available to manage the system. You can easily change the charging parameters once a month to have it go to 100%, then reset the charge parameters the day after.

The lifespan of LiFePo4: We don't know the long-term perfect use cycle-life for it yet. The battery is, in operation, a chemical reaction. Over time the performance of the system will degrade. For a properly cared for system, like yours looks to be, it will likely outlast 5 years if not far longer. By that time you will likely want to replace it with something better.

As to your question: "What counts for a cycle?"

You will get different answers on who you ask. In most off-grid systems, we could count 1 full cycle a day, and about 10-20 "mini-cycles" (DoD 20-50%). For each application, the pack will perform differently over the years. I've heard good things about Victron's own product and the manufacturer they use is one of the highest quality battery companies in China.

A 3 year example of a heavily used LiFePo4 system:

I have been using a LiFePo4 48v 200Ah pack since 2017. LiFePo4, in general is a very hardy, resilient chemistry able to withstand abuse on occasion.

In my example, we have been putting the 200Ah pack through at least 1 full cycle a day (95% down to 20%). I charge based per cell of 3.55v and discharge down to 3.0v. However, it is a rare occurance outside of winter where we discharge that far down. Still - for 4 months of the year, we are doing full DoD down to 20% and then our generator charges it at 0.2C back to 95%. Some days, this occurs 2 to 3 times a day. Indeed, this battery pack is undersized for the usage pattern it has been pressed into.

In addition to this, the pack will undergo 4-6 mini-cycles each day. Perhaps drawing 25-75ah each time. This is due mainly from electric appliances. Clothing dryer, washer, water pump, inductive cooktops.

Real capacity, after 3 years, stands at 170Ah. 85% capacity after 3 years of hard use. I have also had to switch out 2 of the cells that lost capacity at a far faster rate. This was not a Victron battery pack and was a DIY.

I would expect your system, and most systems that are sized better for the usage pattern, to perform far better.

Jason Bolduc

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kevp avatar image
kevp answered ·

This is a great question and a great answer from Jason above. I have also been wondering how to get the best from my investment. I have a motorhome which has been used little in Covid times due to the restrictions in place in Germany where I am currently living. I used the Victron Smart App to create a preset, which I called storage. It sets the Bulk value to 13.2v and float to 13v. This means that the solar will allow the battery to fall to mid charge and stay there for the extended not in use period. When sanctions are lifted, I will select the LifePO4 preset and it should top itself up. Let me know if anyone can see a flaw in this plan.

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