> where do you source those batteries? The cheapest ones that will fit in the ups from amazon with a decent rating.
I literally use a tape measure to measure the old dead lead acid batteries to see what will fit. I have found that I can get batteries with more amp hours than the lead acid replacements. I figure even if the manufacturer is crap will outlast LA battery technology. - J On Fri, Apr 11, 2025 at 4:52 PM Mark Tinka via NANOG <[email protected]> wrote: > > > On 4/11/25 17:40, Gary Sparkes wrote: > > > 30% being a reasonable floor absolutely is true. > > > > I didn't say 30% DoD was unreasonable. I said that claiming that going > below it to 20% is dangerous is not true. > > But, happy to agree to disagree. > > > > Far less stress to go 100 to 30 and back to 100, then 90 to 20 and > > back to 90, etc. Keeping 30 as an operational floor lets you use full > > capacity as needed and remain at full functional charge with maximum > > lifespan retention/recovery. > > > > That can be said of any charge/discharge window if you are not > consistently discharging below a given threshold, whatever that is to you. > > > > EV’s charge/operate that way to extend pack lifespan primarily. > > > > Right, but the key motivation for that is for the car manufacturers to > meet warranty claims, normally at least 10 years. And they will remotely > manage those charge/discharge profiles to put warranty objectives over > range maximization. > > > > 4.2v float is fine if you aren’t routinely low end stressing it. > > > > 4.2V float is for NMC. LFP is usually around 3.5V float. > > > > Yes, the internal resistance bit is true, but that really does start > > to kick in around 25-30. A lot of datasheets I’ve worked with talk > > about 30% and stress zones. > > > > Internal resistance in Li-Ion cells is highest as the battery approaches > a fully-charged or fully-discharged state. In other words, internal > resistance is highest at 100% SoC and below 20% SoC. But since we know > that Li-Ion batteries have a non-linear voltage curve until about 10% > SoC, internal resistance is most dangerous below this SoC value. > > > > Far better to remain at 100% float for battery lifespan than to > > routinely dip below 30%. > > > > In my experience, not going below 20% SoC will be better than holding a > 100% charge for an extended period of time, especially if you are not > actively controlling ambient temperature. > > Li-Ion batteries really do not like holding a full voltage for too long, > although, for me, that would not be as bad as routinely running an SoC > below 20%. > > > > Calendar aging is not as cut and dried as it may seem. This is > > blatantly obvious with cellphones, of course, but holds true for lots > > of other implementations too. > > > > Li-Ion batteries have a completely different use-case for cellphones > than for home backup, because we prioritize capacity and peak > performance for cellphones vs. home backup. This is why it is quite > normal for people to expect their phone battery to be pretty "useless" > after an average of 3 years. > > > > I expect 90% capacity on 10-year-old batteries stored properly almost > > always, usually – at a minimum. > > > > Again, stored batteries have no value to anyone :-). > > The better metric is how to maintain working batteries for 10 years and > see how much capacity you've retained by that time. > > > > > > But cycle durability is what truly matters in the long run for > > lifespan, not calendar aging, for batteries that often see use. And > > 30% is a sweet spot between usable capacity and lifespan extension to > > often double the manufacturer’s rated cycle count. > > > > Yes, we all want cycle durability, but calendar aging is unavoidable. > And since the biggest contributor to calendar aging is ambient > temperature, most owners will lose capacity due to that because they do > not have active cooling for their batteries. > > I disagree with 30% being a recommended DoD floor (most OEM's do not > suggest that), but that's okay :-). > > > > Remember, cycle count means you’re actually using it – so I’m not > > charging or discharging any less, only doing so to specific levels. > > > > Li-Ion batteries are not cheap. People will always prioritize capacity, > and the money to buy a larger pack just to save 10% from your discharge > cycle does not justify the extra longevity in environments where most > people will let batteries overheat. > > > > I’d also point out a lot of research is also indicative of low > > discharge levels being the leading factor to degradation, not capacity > > float charge status. Heat is the the number one factor (outside of or > > at high end of design spec heat, as often seen in consumer devices). > > Low discharge is factor #2. High / full charge stress comes in around > > #3. Better to engage #3 than #2 or #1 for lifespan retention. > > > > Maintaining a long term 100% SoC state is not problematic if you can > actively cool your battery. Most owners will not, which is why this can > be more damaging to your battery than a low SoC. > > Remember, most batteries will spend the majority of their life closer to > 100% SoC than at 1% SoC. > > Mark. > _______________________________________________ > NANOG mailing list > > https://lists.nanog.org/archives/list/[email protected]/message/S4CZUXPXIQDP3EQSK4CQUBSDH4AMLMNP/ _______________________________________________ NANOG mailing list https://lists.nanog.org/archives/list/[email protected]/message/AY2K4WBTINZOAXS27WKXUW7LFNCC7MNT/
