CPAPGuide
LiFePO4 vs NMC batteries in portable power stations
What the two lithium chemistries in power stations actually change for you (weight, cycle life, heat and cold), how to tell which one a station uses, and why it doesn't change our runtime numbers.
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- 3 power stations
- 1 device
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This page sizes a power supply. It is not medical advice. Check your CPAP manual and talk to your equipment supplier before relying on battery power overnight.
If you’re buying a power station now, we’d lean LiFePO4. It’s heavier for the same capacity, but it lasts through far more charge cycles and it’s the more forgiving chemistry when things get hot. NMC still makes sense if every pound counts and you won’t cycle the battery often.
What the letters mean
Both are lithium-ion batteries. The name tells you what the cathode is made of.
- LiFePO4 is lithium iron phosphate, often shortened to LFP. Spec sheets write it either way.
- NMC is lithium nickel manganese cobalt oxide. You’ll also see it as NCM, or as “ternary lithium” on some listings.
If a listing just says “lithium-ion” and nothing else, check the manual. It usually names the chemistry in the battery or specifications section. On a used or clearance unit, check the manual for that exact model and version, not just the current product page.
Every station in our data is LiFePO4, from the little EcoFlow RIVER 3 up to the EcoFlow DELTA Pro. That’s just what we’ve added so far, not a survey of the market, but it does mean we can’t put an NMC station side by side with a LiFePO4 one in a table yet.
Weight
NMC stores more energy per pound. Put the same number of watt-hours in both chemistries and the NMC pack is lighter and usually smaller. That’s NMC’s main advantage.
For a station that lives in a van or by the bed, the extra weight doesn’t matter much. For one you’re hauling to a campsite from the parking lot, it might.
Cycle life
This is the big one. A cycle is roughly one full battery’s worth of charging and discharging, whether that’s one deep cycle or a few partial ones that add up. Every lithium battery loses some capacity each cycle, and LiFePO4 loses it more slowly. LiFePO4 stations are usually rated for far more cycles than NMC ones.
When you compare cycle ratings, read the fine print. A rating is the number of cycles until the battery drops to some fraction of its original capacity, and that fraction, and the test conditions, vary between brands. One brand’s figure isn’t directly comparable with another’s unless they test to the same end point.
If you charge the station once a month for a blackout kit, either chemistry will probably age out from time before it ages out from cycles. If you run a CPAP off it every night, or cycle it daily from solar in a van, cycle life is the spec that matters most.
Heat and safety
LiFePO4 is more resistant to overheating and thermal runaway than NMC. That’s a property of the chemistry. Any lithium battery can fail if it’s damaged, charged wrong or cooked, so keep it out of a closed car in the sun, don’t block the vents, and use the charger it came with.
Cold
Neither chemistry likes being charged below freezing. Charging lithium cells that cold can damage them, and the manual gives the charging temperature range for that station. Some stations protect themselves by refusing to charge until they warm up. Both chemistries also give less capacity when they’re cold, so a station sitting in a freezing van will run your things for less time than the tables say.
What it doesn’t change: our numbers
Chemistry doesn’t change how we calculate runtime. A watt-hour is a watt-hour, so we take the rated capacity, apply an efficiency factor for the power path and divide by the load. For example, a ResMed AirSense 11 on the EcoFlow DELTA 2 over 12V comes out at 16.5 hours. An NMC station with the same 1,024 Wh rating would get the same calculated figure.
Where chemistry shows up is later. Our runtimes are for a battery at its rated capacity, which in practice means a new one. After a few years of nightly use, an NMC station will tend to have lost more of that capacity than a LiFePO4 one, so its real hours will drift further below our tables. We explain the other reasons real runtime differs from the math in watts vs watt-hours, and the formula itself is on our methodology page.
Storing it
Whichever chemistry you have, don’t leave it full and hot for months. The manual says what charge level to store it at and how often to top it up. And if the battery percentage on a LiFePO4 station seems to jump around, that’s partly the chemistry: its voltage barely changes across most of the charge, so the station has a harder time estimating it. The manual may suggest a full charge to recalibrate.
If you’re choosing between two stations that are otherwise close, and one is LiFePO4, we’d take that one.