LifePo4 in winter

[Bob S]

Getting ready for winter in New England. I will be removing my 2 batteries to bring inside. I came across an interesting read on the DIYsolar forum.

How to Find Happiness With Lithium-ion batteries (LiFePO4)

Lithium-ion batteries, (LiFePO4) how to charge, discharge, maintain and prevent damage for maxium life and capacity.

www.solacity.com

My limited understanding is freezing temperatures will damage these batteries yet towards the bottom of this article "Storing Lithium-Ion Batteries"
contradicts my understanding. What are your thoughts? It would be a lot easier to disconnect the batteries from all loads and charging sources and leave them on the boat. In my case the boat sits in my yard and can easily be inspected once a week. Not sure if the Overkill Solar app can shut off the BMS from it's small draw or even if that's necessary.

 

[Davidasailor26]

Generally storing lithium in cold temperatures is fine, but charging them below freezing is definitely not. Check your manufacturer specs on minimum storage temperatures. Most lithium batteries allow a storage (but not charging) temperature well below 0. Some have a higher minimum temperature, though I’ve not seen a reason why they differ.

 

[dlochner]

Here's another article on the topic, from Panbo.com.

Don't murder your batteries, tips for winter storage of LFP batteries

Learn how best to store your LFP batteries during a layup. Make sure your batteries aren't damaged during extended storage.

panbo.com

 

[Hayden Watson]

USING LFP batteries at freezing temperatures will not harm them. The problem is CHARGING them below freezing. Many BMS's have low temperature cutoff and if you are in an area where you can have below freezing temps, this is a very good thing to have.

The cells can discharged and stored down to -20ºc or -4ºF. If your storage temperatures are less than that, it is best to remove them and store in your house.

 

[marcham]

Charge / discharge them to 60 pct, disconnect all loads and charging sources.... sleep well until the spring

They travel by truck /shipping container that routinely go well below freezing, they will not be harmed.

 

[Captain Larry-DH]

You will not damage them if stored in your boat in New England. I keep mine aboard in CT and my solar charge controller has a low temperature cutoff set. My battery maker (Relion) has the following temperature recommendations
”LiFePO4 batteries can be safely charged between -20°C to 55°C (-4°F to 131°F). However, at temperatures below 0°C (32°F) the charge current must be reduced, until the temperature is >0ºC (32ºF), as follows:
1. 0°C to -10°C (32°F to 14°F) charge at 0.1C (10% of the battery capacity)
2. -10°C to -20°C (14°F to -4°F) charge at 0.05C (5% of the battery capacity)
LiFePO4 batteries do not require temperature compensation for voltage when charging at hot or cold temperatures.
All RELiON LiFePO4 come with a BMS that protects the battery from over-temperature. If the BMS disconnects due to high temperature, wait until the temperature reduces before using or charging the battery. Please refer to your specific battery’s Data Sheet for the BMS high temperature cut-off and reconnect values.”
PS - I do keep the inverter running all winter to power a cellular router for my security cameras. It doesn’t use much power. There are enough days above freezing to keep it charged.

 

[heritage]

Bob S.. You got me wondering if the Overkill BMS 's can be completely turned off with the app. This is AI's answer.

Google Search

 

[thinwater]

It seems there is not a hard rule not to charge below freezing. It's more complicated than that. This from ReLion (the color is my emphisis):

"The damage to the battery when charging at colder temperatures is proportional to the charging rate. Charging at a much slower rate can reduce the damage, but this is rarely a practical solution. When temps fall between 32 degrees and 14 degrees Fahrenheit, batteries cannot be charged at higher than .1C. When temps fall between 14 degrees and -4 degrees Fahrenheit, batteries cannot be charged at higher than .05C. These charging rates will definitely increase charging duration and complicate the entire process because you may not know how cold it could become during a charging cycle. In some situations, you could be going to sleep in 40-degree weather and waking up to a cold snap at 18 degrees Fahrenheit. If you were charging at a higher rate overnight, the falling temperatures could cause irreversible damage to your battery.
The number one rule when it comes to cold-weather charging is not to charge your batteries when the temperature falls below freezing without reducing the charge current...."

In most cases, charging at less than 0.05C is not practical (60 W into a 100 Ah battery), so it is just as well to call it a rule. Most boat systems are set up with closer to 0.1 to 0.3C, and fast charging of a computer or Tesla is more than that. Most of the data you will find online is for C=0.5-2.0. This allows charging in a few hours vs. a few days.

The solar on my F-24 is so small that in the winter season (low sun angle) exceeding 0.02C would be impossible. It is only for battery maintenance--I day sail. The BMS cuts out at 34F anyway, but it's not likely to see <34F in the bilge when the sun is up anyway. For me, disconnecting is not practical since I sail all winter.

Another solution would be to wire a simple thermostat into the solar leads, if you don't want the BMS controlling this. But basically, that is what the BMS is doing for cold weather protection. Common in most batteries now, I believe, but not earlier ones.

Anyway, just posting some information for discussion. What I would do as the OP depends on details of the installation.