What is C-rate and why is it important?
Recently, I tested a 200 amp-hour LiFePo4 12v battery for a video review I did for my YouTube channel (Timeusb 200ah, posted on this page). Although it was not the main focus of the video itself, during the review I made some comments about C-rate and decided to expand on it here.
It is a fact that LiFePo4 batteries are one of the most misunderstood topics on the internet, with even large “expert” channels spreading and repeating false information. It’s not possible to deal with it all at once. So I’m going to try to help solar power enthusiasts directly by focusing on and providing some simple facts and truths about C-rate. The goal is to help preserve and extend the life cycle of their batteries.
Calculating C-Rate
The “C” in C-rate refers to Capacity in Amp-Hours. So if we have a 200 amp-hour battery, C/10 means Capacity Divided by 10.
For a 200 amp-hour battery, C/10 would equal 20 Amps. A 1C (1 x C) rate would equal 200 amps.
Based on over a decade of experience and research, C/10 has proven to be a perfectly safe rate for both Charge and Discharge of normal LiFePo4 storage batteries. As long as temps don’t drop below freezing, operating at C/10 can never harm the cells in any way.
Energy vs. Power Cells
Storage batteries (like those used for so called Off Electrical Grid, RV, camping, cabins etc.) tend to use Energy cells, not Power cells. Power cells are specially constructed to allow very large current charge and discharge – however they may give up capacity as a result. Energy cells focus on and are constructed for Maximum Capacity. Therefore, it make perfect sense that Energy cells are the most common type in the Storage Battery market.
It is a fact that if you are using Energy / Storage cells, regularly exceeding C/10 will shorten the life cycle of your batteries! I’ve done tests on batteries using 1C (or higher) rates just for research, knowing I was shortening the life cycle. However, the good thing is – even with this abuse, the batteries survived with only diminished performance.
Resiliency of LiFePo4
But the resiliency of LiFePo4 works both ways: sure they can take a tremendous amount of abuse and still survive. But by the time the user notices degradation of capacity and performance, it’s too late. Nothing can bring the lost capacity back – it’s permanently gone.
This resiliency is one of the reasons why many LiFePo4 users think it’s OK to run 1C charge/discharge, because hey, their batteries keep on working! But when the batteries start showing problems and diminished performance later, most will probably never make the connection between that and excessive C-rate cycling.
There’s More…
But there must be more to the story. What exactly causes the damage in LiFePo4 batteries that are subject to excessive C-rate?
I plan to further expand on the technical knowledge behind this topic in great detail via an upcoming video on my YouTube channel – please stay tuned. I hope you found this article helpful.
Thanks for reading! -Dave, SPE
I do not receive commissions for battery sales. Below is a link to Timeusb’s 200ah LiFePo4 battery product, plus a 5% discount code.
5% OFF Code: SolarPower (Valid for Timeusb – All Products)
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