Lithium and Long Term

[FlyStar]

Should I just leave the rv plugged in whilst in months long storage. Lithium batteries and Lithium capable converter. Not freezing temps.

[JKellerJr]

I don't think it matters much. During the season I'll leave ours plugged in regardless of the time between trips. Over the winter I unhook it and disconnect the batteries and let them sit in the unit. (We have a true full disconnect). We do have freezing temps.

I have Battleborn batteries if it matters. Different manufacturers may have different requirements.

[xrated]

Should I just leave the rv plugged in whilst in months long storage. Lithium batteries and Lithium capable converter. Not freezing temps.

Most LFP battery manufacturers suggest that long term storage should be done at some number LESS than fully charged. You will find numbers like 30-70%....maybe 40-60% and then a few...BattleBorn comes to mind here, will tell you it's OK for them to be at 100%. Part of the equation is also what the charger voltage puts out once the battery is fully charged. A LFP battery is considered to be fully charged (or right at it) at 3.45V per cell or 13.8V. So a charger that floats at 13.8V will keep the battery at what is considered to be fully charged.....and that's not recommended for many LFP batteries.

This coming winter will be my first with LFP batteries and I'm going to start out my winter storage SOC at around 60%. Then probably once or twice over the winter storage time I will charge them up...but not fully charged, then drain them down again to the approx. 60% SOC. I have a shunt on my system and can see what goes in and what is used, and that makes things a bit easier that trying to guess or use battery voltage as an indicator. LFP has a very flat voltage curve until you get into the upper and lower knee, so a good shunt will give you a much more accurate reading on battery state of charge.

When I built my battery, I also built a heated/insulated battery box and all I need to do is fire up the battery heaters until the internal temperature of the cells are safe to charge, and then do the charging. I also have a 200W 12V heater that I can hook up to the battery to draw it down...all the while monitoring the battery SOC.

[Ynot4me2]

As I'm reading this thread I'm wondering what is the difference between storing a LFP while plugged in compared to someone that is FT and always uses FHU? Even if they move every now and then, the battery is still being charged by the TV.

[xrated]

As I'm reading this thread I'm wondering what is the difference between storing a LFP while plugged in compared to someone that is FT and always uses FHU? Even if they move every now and then, the battery is still being charged by the TV.

The simple answer is that most LFP batteries do not tolerate full voltage storage very well and keeping them at full voltage when stored will certainly decrease the life of the battery. A "Full Timer" is using the battery....every day and discharging the battery....at least to some extent. Cycling the battery on a daily basis.....using some of it and charging it.....is certainly a lot better for the battery than just sitting at full charge for months. And LFP batteries will certainly self discharge over time, but the rate of self discharge is much, much slower than LA batteries, which really need to have float voltage on them to keep them healthy. LFP batteries, even if stored at let's say 70% state of charge, the manufacturers normally will recommend that they be cycled occasionally during a longer storage period.....say three months or more.

[JKellerJr]

I'm probably a little different than some here, especially those that have built their own like @xrated. They will more of a deep dive into the ideal circumstances for running a lithium and have a lot of good information.

While the main reason was the increased capacity for boondocking another very big reason for me was the "set it and forget it" appeal of lithium. No worries on discharge past 50% or killing one prematurely by draining to empty, etc. I let the BMS do the work and I forget about them. About the only thing I pay attention to is if I am going to see a prolonged period of sub zero temps then I'll throw a heat light of small heater in the compartment where the batteries are since its a real chore to get them out from where I mounted them. But so far that's never happened.

My first set of BB's (2) went 4 years with really no appreciable loss of capacity before I sold them. I wanted to step up to more capacity, BB said I was probably OK just adding to the old ones but I decided to sell the old ones and start anew. Another plus of lithium, I recovered over 50% of the cost of the batteries when I sold them .