Any lithium battery claiming to be rated for operation down to -20 C is likely lying. Lithium chemistries are sensitive to temperature and operate well in a narrow temperature range. Operation below freezing ambient temperatures requires a heater and heaters need energy - hence why they are uncommon and only add cost.
Au contraire, lead-acid batteries work pretty well at temperature extremes, needing only changes in charging (e:) voltage and being limited by discharge current.
Any lithium battery claiming to be rated for operation down to -20 C is likely lying.
Not necessarily lying but rather there are heating pads that use some of the energy to bring the battery up to safe operating temperature based on BMS readings. There are some LiFePo4 battery breakdowns on Will's YouTube channel that show the various heating pads used by each vendor. [1] So probably better to say they leave out some details that will affect capacity at lower temperatures. He has a HN account so maybe he will also comment.
That’s exactly my point though - if you are aiming for robust operation at a wide temperature range, lithium batteries are actually a worse choice than lead acid batteries. Lead acid batteries require little to no temperature control, just some charging rate and voltage control depending on temperature.
I wasn't actually disagreeing with you, just pointing out that at worst the companies are lying by omission. That said I don't think there is a one size fits all. LiFePo4 are great where weight matters more than temperature such as boats, RV's or anything that is mobile. The power used by the heating pads in some cases is offset by the higher capacity and ability to maintain voltage at lower charge state.
For off-grid buildings lead/AGM is fine especially if not depending on solar and perhaps instead keeping a charge from a water turbine from a river or stream. AGM have significantly less charge cycles than LiFePo4 and the disparity is growing more every year. China went both Sodium and LifePo4 due to logistical and shipping issues with some of the materials required in Li-ion. Li-ion batteries also have heating pads. I can't see AGM being viable in solar farms due to the low charge cycle ratings. Either that or whoever the manufacture is will be very happy as those batteries will have to be cycled out quickly.
I have 4 AGM batteries for a few of my inverters that need higher surge capacity in a smaller space and the UPS driver remembers me for it. Now they make me get the batteries out of their truck. Since I keep the AGM's fully charged with commercial power the charge cycles are less of an issue for me and thus the TCO/ROI is acceptable. LiFePo4 current ratings are catching up though. Now I can get one that has a 200+ Amp discharge rating and I am told there will be one with a 300AH/320 Amp discharge rating soon.
I am most curious about what comes next. The 3D printed solid state batteries look very interesting. 50% of the weight for the same capacity, higher C rating, significantly safer. Mass production is just starting for those so time will tell I guess.
The killer feature of lead acid designs is cost and availability. In many applications, they are significantly cheaper. The chance cycle issue is real and i’m glad you brought that up. For some applications, they make sense. One is a low power draw solar-powered website. Lead acid batteries also outlast most lithium chemistries by several years. These batteries have been around for decades now are are absolutely everywhere and the voltages are standardized. that alone is a significant advantage.
Case in point - i run a UPS using my old 12 V car battery. Granted, i cannot keep this indoors but it works well.
Similar to what you said - off-grid or backup power is the mainstay of lead acid designs. almost every electrical substation out there uses lead acid for backup power.
That hasn't really been true for years. At the same temperature, FePO4 outperforms lead acid in voltage, discharge current, and capacity.
> Operation below freezing ambient temperatures requires a heater and heaters need energy.
No. Charging requires a heater, discharging does not. It's really not reasonable to say "operation" requires a heater. While you're discharging, you're worried about the capacity and duration, and running a heater is a huge problem. The slower your discharge, the more of an issue it is to run a heater.
While you're charging, it usually isn't. You're already losing plenty of power to the charger inefficiency, it just takes a little more power to keep it above ambient. If you're plugged in it's irrelevant.
Fair point that only charging requires a heater but how does that meaningfully address the issue of cold weather operation? A battery requires charging and discharging and being able do to one but no the other won’t cut it, surely? The loss of capacity to heat is significant - often 10-30% capacity but that figure depends.
Also, i’m not sure plenty of power is lost to charging inefficiency. most industrial inverters operate at nearly 90% efficiency. Besides, above ambient isn’t a good metric - lithium chemistries do well around 10-25 C. If ambient is - 5 C, a delta of +5 C doesn’t change my core point.
Even if you are plugged in, lithium batteries aren’t dissipating heat. Not sure what the charger inefficiency has to do with this because that heat often isn’t the batteries themselves.
> The loss of capacity to heat is significant - often 10-30% capacity but that figure depends.
But it isn't a loss of capacity (although there is also a loss of capacity due to cold, in any chemistry). The capacity is the same, it just takes more energy to put the same amount of energy in. If you are putting energy in, you usually have an oversupply, and heating the battery is not an issue.
> If ambient is - 5 C, a delta of +5 C doesn’t change my core point.
I used the phrase "above ambient" specifically because the battery does not need to be warm unless you need to charge it quickly. If it's above 0 Celsius, it can charge. The warmer you make it the faster you can charge it. If the wasted energy is an issue you can charge slower.
> most industrial inverters operate at nearly 90% efficiency.
An inverter is significantly simpler than a battery charger. FePO4 charging can start as low as 2.5 volts and go past 3.6 volts. Making a converter with a 50% swing in voltage is not particularly easy. This higher-end charger picked at random[1] drops to <75% efficiency at the end of charge.
GP said rated, not necessarily for operation. It could just mean that the battery will survive such low temperatures unharmed.
I have a summer cabin with a solar panel and a couple 12 V lead acid batteries. It would be great to be able to install some lithium type batteries instead, so long as I know they will survive winter.
Au contraire, lead-acid batteries work pretty well at temperature extremes, needing only changes in charging (e:) voltage and being limited by discharge current.