LifePO4 Long-term Storage

[futureproof]

Have a 12v LifePO4 battery in a truck camper (120ah). Existing converter wired is the old ELX-20, which charges at 13.4v - period. My thought is that this is actually a good voltage for long-term storage, if I leave the batteries at 40-70% of capacity, and then leave the camper plugged into shore power with the constant 13.4v that will float the LifePO4 battery at a healthy state for maximizing lifespan, versus the "battery full/ready to go" approach.

Then, I can always connect my true LifePO4 charger to the battery terminals if necessary to get the battery up to a full charge. Or if I just hop in and start driving, the DC-DC charger will top off the battery on my way to my destination. Plus, I have a solar suitcase with LifePO4 controller. So, really, the old school converter is fine for this "float" long term storage use case, right?

Make sense to people, or should I just eventually replace the converter to a LifePO4 version?

 

[koobs]

Unless you have a parasitic drain on the battery, you don't really need a float. They say you shouldn't leave trickle chargers on LiFePO4 anyway.
I'd leave it unplugged and top up charge every 6 months or so.

 

[Capt Bill]

Have a 12v LifePO4 battery in a truck camper (120ah). Existing converter wired is the old ELX-20, which charges at 13.4v - period. My thought is that this is actually a good voltage for long-term storage, if I leave the batteries at 40-70% of capacity, and then leave the camper plugged into shore power with the constant 13.4v that will float the LifePO4 battery at a healthy state for maximizing lifespan, versus the "battery full/ready to go" approach.

Then, I can always connect my true LifePO4 charger to the battery terminals if necessary to get the battery up to a full charge. Or if I just hop in and start driving, the DC-DC charger will top off the battery on my way to my destination. Plus, I have a solar suitcase with LifePO4 controller. So, really, the old school converter is fine for this "float" long term storage use case, right?

Make sense to people, or should I just eventually replace the converter to a LifePO4 version?

Have a 12v LifePO4 battery in a truck camper (120ah). Existing converter wired is the old ELX-20, which charges at 13.4v - period. My thought is that this is actually a good voltage for long-term storage, if I leave the batteries at 40-70% of capacity, and then leave the camper plugged into shore power with the constant 13.4v that will float the LifePO4 battery at a healthy state for maximizing lifespan, versus the "battery full/ready to go" approach.

Then, I can always connect my true LifePO4 charger to the battery terminals if necessary to get the battery up to a full charge. Or if I just hop in and start driving, the DC-DC charger will top off the battery on my way to my destination. Plus, I have a solar suitcase with LifePO4 controller. So, really, the old school converter is fine for this "float" long term storage use case, right?

Make sense to people, or should I just eventually replace the converter to a LifePO4 version?

In wondering about best voltage for LiFePO4 Storage, and not finding much specifics via an Internet search; ... I emailed sales at battlebornbatteries a Question: ... for your 12v 100 Ah LiFePO4 ... Do you have a battery storage voltage recommendation for long term storage when disconnected from all cables and devices? Just wondering if full is ok, or maybe 70% is better for storage. Jody replied from a dragonflyenergy.com email address (they sell battleborn) with this Answer: "For storage purposes we would recommend fully charging your batteries up to 100%, 13.6 or above. Then disconnecting them from the system. This way they can sit there in temps down to -10 degrees F for up to a year. If you anticipate the temperature getting colder than that, we would recommend moving them into a more temperature controlled environment. " My Reference Note: My newest order of 280 Ah EVE cells arrived at 3.301v, which is about 70% SOC. In contrast, this Battleborn info. would translate to 3.4v or above. I think I would go with the battleborn reference. Bet 70% works too in non freezing temps. Wonder what other opinions are out there/ especially from the suppliers. ;+) Bill

 

[sunshine_eggo]

It also depends on temperate. Hot temperature + high SoC = faster degredation vs. low temperature + high SoC. My EVE cells indicate 30-50% and discharged/charged once every 6 months.

A BMS will have a continual draw on the cells, so it will lose charge faster than standalone cells. That's why most battery manufacturer's indicate to fully charge every X months.

13.4V float will likely maintain a fully charged battery at full charge. I let 9 LFP 280Ah Eve cells sit for 5 months after fully charging, and most were above the 3.35V average 13.4V would yield with no significant loss of SoC (<0.3%). ONE of the cells in that group settled to 3.30 with a 1% loss in capacity. At 13.4V, that cell would have received charge.

13.6V float will get LFP to 95% SoC.

IMHO, 13.4V is too high to ensure the 40-70% SoC you're targeting. I would discharge the battery to 50% and then connect to the charger. Determine what the end SoC is after a week or so.

 

[jharrell]

Everything I can find on LFP shows SOC is a minor factor in aging while high temperature is the major factor. Also low voltage is the killer in storage, this is why Battleborn recommends a full charge then store in cool place which will allow the longest amount of time until self discharge causes an issue. Battleborn also is ok with floating because again high SOC does very little to accelerate LFP aging assuming lower temperatures and it prevents LV.

Perfect long term storage would be floating at around 13.1V which will keep the SOC down but never too far down, I float at 13.6V so my batteries are ready to go at any time and they should outlive my RV at this point.

 

[Capt Bill]

It also depends on temperate. Hot temperature + high SoC = faster degredation vs. low temperature + high SoC. My EVE cells indicate 30-50% and discharged/charged once every 6 months.

A BMS will have a continual draw on the cells, so it will lose charge faster than standalone cells. That's why most battery manufacturer's indicate to fully charge every X months.

13.4V float will likely maintain a fully charged battery at full charge. I let 9 LFP 280Ah Eve cells sit for 5 months after fully charging, and most were above the 3.35V average 13.4V would yield with no significant loss of SoC (<0.3%). ONE of the cells in that group settled to 3.30 with a 1% loss in capacity. At 13.4V, that cell would have received charge.

13.6V float will get LFP to 95% SoC.

IMHO, 13.4V is too high to ensure the 40-70% SoC you're targeting. I would discharge the battery to 50% and then connect to the charger. Determine what the end SoC is after a week or so.

I just got an opinion from a long time motorcycle buddy I respect for his mucho solar and battery tech experience telling me 80% SOC, or a bit less / for long term LiFePO4 storage is the way to go. I think I will respect that info. .. I am also planning to fully disconnect my battery bank from all current draws including my DIY LiFePO4 build's self installed BMS (why not?) ...

 

[futureproof]

Thanks all. Since the original post, I've decided I will rarely (or never) use the older converter for float purposes at 13.4v and to avoid any sort of notions around a trickle or float for the LifePo4 battery (but leave the older converter in place, because why waste money on a new converter). I have a battery disconnect that I use so when the older converter is on shore power putting out 13.4v, I can disconnect from the battery for long term storage and let the 12v battery sit at a nice "storage state" around 40-70% This way I can run out to the camper during the winter and use shore power for the AC and 12v DC system without involving the LifePo4 battery. (Sometimes I am in there when parked in the off-season, since it's kind of a man-cave project area, or I am working on something in particular.). The old Elixir converter is still semi-useful if I ever decide to keep 13.4v going into the house LifePo4 battery to work it up towards 100% SOC before a different LifePo4 capable charger takes over, or at least to supply power to the house 12v system when the battery is offline.

Then, generally, when I want to get the 12v LifePo4 battery to full charge, I use one of the following:
1. Battery charger on AC power.
2. Victron DC-DC charger while driving.
3. Solar charger.

My main problem now is that I am still using my camper sporadically during the winter and colder months, and running into issues with LifePo4 temps. Need to figure out a long term solution that keeps the LifePo4 battery in a position so that I can use it during the winter, but I cannot simply keep it warmer all the time. I have many components purchased standing by for some sort of solution, including the sticky heating pads, temp sensor relays, voltage sensing relays, and even a higher amp 12v heater for a quick flash heat (that may not get used). (I already swapped my lead acid back in twice for short winter trips where I didn't feel like dealing with cold temps and LifePo4.). Probably just going to throw some sort of master switch on a low amp heating system that can be turned on a day or two before a trip and keep my LifePo4 in a warm enough state to charge/discharge during winter use. The heating system just has to be used in a setup where I know I can produce enough charging power to keep the battery heat running when necessary AND use the batteries. Long as the charging input outweighs the discharge to heat the battery, it's all good (such as driving with DC-DC). Or use some sort of lightweight heater on a relay that works when the alternator is running.