Portable Power Station vs Batteries

[Alex]

Hi,
Why are LifePO4 batteries rated in Amp Hours while Portable Power Stations rated in Watt Hours? How would you compare the two? If you had a 100 Amp Hour battery, what size Portable Power Station would be the equivalent?
Thanks.

[JRTJH]

Here's the "general rule" :

1 watt-hour is defined as 1 watt of power expended for 1 hour. 1 amp hour is defined as 1 amp of current expended for 1 hour.

So, at 13.6 VDC, there are 13.6 watts in every amp.

A 100 amp hour battery that's fully charged and providing 13.6 VDC is equivalent to a 1360 watt hour battery. (13.6 x 100 = 1360)

Two 100 amp hour batteries that are fully charged and providing 13.6 VDC is equivalent to a 2720 watt hour battery. (13.6 x 100 x 2 = 2720)....

Where the formula gets "wonkey" is when you start trying to calculate amp/hour or watt/hour variations as the battery voltage drops as the charge drops.... Since lead acid battery voltage drops at a different rate from a lithium battery, the "direct correlation" is, at best, hard to calculate. So many (probably most) don't attempt to "calculate the slight differences between battery bank technology.

[Alex]

Thank you for the great explanation!

[snoobler]

Originally Posted by Alex

Hi,
Why are LifePO4 batteries rated in Amp Hours while Portable Power Stations rated in Watt Hours? How would you compare the two? If you had a 100 Amp Hour battery, what size Portable Power Station would be the equivalent?
Thanks.

Ah is only meaningful in the context of VOLTAGE, i.e., 100Ah @ 12V.

Wh is a measure of energy independent of voltage. It equals Voltage * Ah.

Batteries have a specified nominal voltage depending on cell count and chemistry, so Ah is a common measure of capacity. I emphasize nominal because that's the voltage used to compute Wh, e.g., a 12V 100Ah lead-acid battery has 1200Wh, not 13.6V * 100Ah. A "12V" LiFePO4 (LFP) battery is actually 12.8V nominal, so they have 1280Wh for a 100Ah "12V."

Power stations may be at 12, 24 or 48V on the inside. You're not tapping the battery directly, so Ah tells you nothing, and it's more sensible to quantify the total energy in the storage device as Wh.

If you want to compare apples to apples, always convert to Wh.

Again, Wh = Nominal Volts * Ah.

Lastly, note that "power stations" will typically only deliver about 70-80% of their rated Wh. The circuitry inside them consumes power to generate the features provided. If you leave a power station ON with no loads attached, it will likely consume all of its own capacity in a few days to a couple weeks depending on battery/features.

[Alex]

Again, thank you for explaining "why" they are rated differently. I never could grasp it.

[mikec557]

Originally Posted by Alex

Hi,
Why are LifePO4 batteries rated in Amp Hours while Portable Power Stations rated in Watt Hours? How would you compare the two? If you had a 100 Amp Hour battery, what size Portable Power Station would be the equivalent?
Thanks.

I learned something about "portable power stations" this past Fall. Specifically, I learned about it having bought a 720Wh EcoFlow. And I think it's true about all of them.

Do not be misled into thinking these are a "12v source". They're not. It seems each manufacturer is different, but in general the battery pack in any of them is between, about, 20v and 26v.

That means you are powering an internal CONverter to reduce 20vdc(ish) to 12vdc. And just like an INverter, you're burning up power in overhead to MAKE 12v, and of course to make 5v for the USB outlets.

That means I never came close to getting 720Wh of 12v.

If you can live without the convenience of the packaging of the power station, you're better off with a 12v lithium iron 100ah or 50ah battery.

One other thing to watch for is the battery chemistry in the power station. Some are lithium iron, but many are lithium ion. That's a difference of 2000-5000 recharge cycles or getting 800ish recharge cycles.

[Alex]

This is very good info. I for one, am learnig a lot.
Thank you.