question

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: (https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/ )

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

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.