diy solar

diy solar

Using LifePo4 as an emergency back up

J-dog

New Member
Joined
Aug 29, 2021
Messages
1
Hey guys, if I were to use a LifePo4 in an emergency backup situation, what would be the shelf life of the battery? It could sit around and technically never be used for decades if you know what I mean. Of course I would have to keep it charged because of it sitting from lack of use. I'm new to solar backup systems and I didn't want to invest in something that wouldn't be there for me 10 years from now. There's much discussion in forums about cycle life of LifePo4 batteries, but I couldn't find anything on shelf life with a recharge maybe once a year. Thank you in advance!
 
I have no idea how to use a lithium battery as a emergency backup. No spec sheet I see days to do this. There’s always a store at 50% or below.

Flooded lead acid says to leave disconnected for 30 days or longer, but needs to be checked to not go below a threshold around 75%.

I hear Gel is made for that, but when I check the specs of gel cells, does not seem to be the case that they can be left o float for years at a time.
 
While LiFePO4s self-discharge pretty slowly they degrade a bit when held at 100%. During hurricane season I keep mine charged at 80% (and charge them to 100% before a storm). Out of season, I keep them at 60%. This is because of the thread SoC degradation of LiFePO4. Even without that, they'd last 1000s of cycles so it's probably a bit silly. Keep in mind most BMSes need 100% to work (I periodically boost mine).

Lead loves to be at 100% and is therefore great for emergency backup. But, it has to be pretty much be kept on a trickle charger because they self discharge much faster and that one time it gets low for a couple of months pretty much destroys it.

What I'd say for your LiFePO4s is to measure the degradation. That is charge them to what you're happy with, then test the voltage month by month to get the actual degradation rate. Then you'll know what to set up as a recurring manual charge schedule in your calendar.
 
I'll agree with lead for backup. I had an agm cranking battery in my jetski on a maintenace charger for over 10yrs, it started strong every time. I actually went through 3 chargers in that time.
 
Back
Top