[NANOG] Re: Small Capacity UPS

[Gary Sparkes via NANOG <nanog () lists nanog org>]

“30% is not a reasonable floor to stop discharging a Li-Ion battery. All you are doing there is limiting your available 
capacity. The recommended floor to stick to is 20%. However, it is perfectly fine to go as low as 10% without any 
appreciable loss of overall capacity. And in an emergency, you can even go to 5% and still maintain good long term 
capacity.

This is where Li-Ion outshines LA by a mile.

Limiting your capacity by not discharging to, at least, 20% SoC, is quite pointless based on all the information we 
have so far, because calendar aging is still going to get you either way.”

This is… not quite correct.

Age can be mostly mitigated by proper storage – at around 40% SoC for storage charge. I routinely pull out 15-20 (and 
older!) packs that were manufacturer properly storage charged and once jumped up a bit return with 80-90% capacity!

But 30% is a reasonable floor for normal usage, going below that IS a stress zone for the battery – you sharply reduce 
the number of possible full cycles if you delve into this range regularly.

Obviously, when you actually need to use the battery, use it up entirely, that’s what it’s there for. This guideline’s 
more in general in terms of if you can stop at that point, you really, really should do so.

For what it’s worth, I was misremembering the floors slightly. It was 40% and 20% I remember, where stopping discharge 
at 40% gave you nearly *double* the number of full cycles compared to a 20% discharge. IE say you get 600 if you 
routinely go to 20%, routinely going to 40% could net you 1500 instead.



From: Mark Tinka <mark@tinka.africa>
Sent: Thursday, April 10, 2025 1:12 AM
To: Gary Sparkes <gary () kisaracorporation com>; Vasilenko Eduard <vasilenko.eduard () huawei com>; North American 
Network Operators Group <nanog () lists nanog org>
Subject: Re: [NANOG] Re: Small Capacity UPS


On 4/9/25 14:27, Gary Sparkes wrote:


Long term storage, of course, is different, but that's a much easier solved problem, and design specs are often in the 
-30c to 25c range for optimal capacity retention over long term storage. But operationally, 25-50c is perfectly fine. 
Past ... above 5c, I think, you're looking at a 10% capacity fluctuation in that 5c to 50c range.

Yes, most LFP batteries will work even at 60°C, but that does not mean you should do it if you want to get the most out 
of your investment.

The biggest issue is battery aging, and keeping it within recommended temperature values will ensure they last longer 
than if you don't.






While true, heat is the enemy of lithium batteries of any type, deep discharging is the second worst enemy (BMS 
prevents actual cell damaging deep discharge, but you really should never go below 30% of rated capacity if you can 
ever help it - this is the most stressful zone), then charging too rapidly - too high rate of charge.

The point of the BMS is to prevent you from operating your battery in dangerous territory.



Mark.
_______________________________________________
NANOG mailing list 
https://lists.nanog.org/archives/list/nanog () lists nanog org/message/FAN7ADDLGM7TS3R2RXM6NVLI3FP7EG4T/