I get that, for a house/solar battery, it sort of makes sense as your typical energy usage would be measured in kWh on your bills. For the smaller devices, though, the chargers are usually rated in watts (especially if it’s USB-C), so why are the batteries specified in amp hours by the manufacturers?
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In RC hobbies like quadcopters or whatever, we care about voltage (directly or indirectly, like 4S = 4 LiPo cells = ~16-17V) and can use mAh to directly compare between batteries of same cell count.
People intuitively (if not explicitely) understand a 6S 1000mAh battery has a lot more capacity than a 4S 1000mAh.
Yeah we could use watt-hours instead but since we also always care about battery voltage (more than overall battery capacity) it doesn’t matter. It is implicit in the specification (4S 1000mAh, 4S 750mAh, 6S 1200mAh, 1s 300mAh, etc).
mA is a measure of charge, or approximately how long a battery can last.
kW is a measure of power, or how much energy the battery provides.
The phone industry has pushed the agenda more mAh is better, but this isn’t necessarily true.
There are more factors to consider when purchasing a phone, and energy should be a huge factor.
If the phone can’t store more energy (bigger battery, better power management), all the mAh won’t matter as the phone will drain quickly.
The main reason is that small batteries cannot give out amperes worth of current. The flow is generally in 10s of milliamps (the draw the device will need). Bigger batteries, like a car battery, have to give out a few Amps at max need (to start the car is about the biggest current draw). So, the capacity of the battery is discussed at the scale it is used for. It “could” be discussed using decimals instead (0.001 Amp versus 1 milliamp) but we tend to want numbers bigger than 1 rather than decimals. Just easier for average person to imagine 1000 of something than it is to imagine 0.001 of something, or the reverse, 10 of something is easier to deal with than 1,000,000.
This is the same idea behind someone saying “x million gallons is equal to 1000 olympic swimming pools” (whatever the conversion would be, I don’t want to look it up) when talking about the water flowing over a waterfall, as an example.
We “could” give the 3200 mAh battery as 0.0032 kAh, or 3.2 Ah, but people like 3200 better than 0.0032 when doing calcs in their heads. The device draws 30 mAmps per hour and has a 3200 mAh capacity, so we can get about 100 hours of use from it. Way better than doing “the thing has a draw of 0.03 amps and has a 3.2 Ah capacity so I can get about 100 hours of use from it”.
With chargers, you may have noticed that the time to recharge a battery is way less than the time of use that same battery generally gives. This is because the charger gives way more current than the battery is required to give when in use. So, it is “appropriate” (useful) to talk about a 3 amp charger, which would need a couple-few hours to charge that same 3200 mAh battery (because it does not give 3 amps the entire time of charging, just when it can give the max-the battery will not take 3 amps the entire length of the charge, usually). They “could” call it a 3000 mAmp charger. But why, when 3 amps does the same?
In RC hobbies like quadcopters or whatever, we care about voltage (directly or indirectly, like 4S = 4 LiPo cells = ~16-17V) and can use mAh to directly compare between batteries of same cell count.
People intuitively (if not explicitely) understand a 6S 1000mAh battery has a lot more capacity than a 4S 1000mAh.
Yeah we could use watt-hours instead but since we also always care about battery voltage (more than overall battery capacity) it doesn’t matter. It is implicit in the specification (4S 1000mAh, 4S 750mAh, 6S 1200mAh, 1s 300mAh, etc).
Measuring it in ampere-hours works fine as long as the batteries (as a complete unit) are roughly of the same voltage, which is the case for most phones, as the vast majority use one single lithium-ion battery cell, and lithium ion based chemistries have very similar voltage levels.
It doesn’t work when you compare batteries of wildly different configurations, such as 100 Li-ion cells in parallel, or 10 sets of 10 cells in parallel which again are connected to form a serial battery that outputs 10x the voltage. Or batteries consisting of cells with entirely different chemistries such as lead acid (2.1V per cell) or NiMH (1.2V per cell).
To compare these, you need to use watt-hours instead to get a useful number.
Nothing is measured in just mAh, that’s just an abbreviation.
A battery’s capacity is listed as #V###Ah. Like a 3.7V-2400mAh phone battery, or a 12V-7Ah car battery.
Since all phone batteries operate at the same voltage (3.7V for Li-Po), people just leave that part out.
They could do the same for car batteries, since 99.9% of cars use 12V batteries. But I have never seen any car batteries labeled in just mAh (or Wh for that matter).
For house batteries it would normally once again be V x Ah. For example, we had 2 x 12V200Ah batteries in our house, or 24V200Ah total. I have no idea what the actual voltage specs for tesla powerwalls are. In case of a house it makes sense to convert the V x Ah to kWh, since your house runs at 110V or 220V, and the 24V number will be meaningless, and your AC devices will list their power consumption as watts anyway.
mA is a measure of charge, or approximately how long a battery can last.
kW is a measure of power, or how much energy the battery provides.
The phone industry has pushed the agenda more mAh is better, but this isn’t necessarily true.
There are more factors to consider when purchasing a phone, and energy should be a huge factor.
If the phone can’t store more energy (bigger battery, better power management), all the mAh won’t matter as the phone will drain quickly.
Nothing is measured in just mAh, that’s just an abbreviation.
A battery’s capacity is listed as #V###Ah. Like a 3.7V-2400mAh phone battery, or a 12V-7Ah car battery.
Since all phone batteries operate at the same voltage (3.7V for Li-Po), people just leave that part out.
They could do the same for car batteries, since 99.9% of cars use 12V batteries. But I have never seen any car batteries labeled in just mAh (or Wh for that matter).
For house batteries it would normally once again be V x Ah. For example, we had 2 x 12V200Ah batteries in our house, or 24V200Ah total. I have no idea what the actual voltage specs for tesla powerwalls are. In case of a house it makes sense to convert the V x Ah to kWh, since your house runs at 110V or 220V, and the 24V number will be meaningless, and your AC devices will list their power consumption as watts anyway.
An 18650 cell might be 3400-mAh, which is the same as 3.4-Ah.
When a house battery has 300,000-mAh, it gets easier to compare mentally when you call it 300-Ah
Measuring it in ampere-hours works fine as long as the batteries (as a complete unit) are roughly of the same voltage, which is the case for most phones, as the vast majority use one single lithium-ion battery cell, and lithium ion based chemistries have very similar voltage levels.
It doesn’t work when you compare batteries of wildly different configurations, such as 100 Li-ion cells in parallel, or 10 sets of 10 cells in parallel which again are connected to form a serial battery that outputs 10x the voltage. Or batteries consisting of cells with entirely different chemistries such as lead acid (2.1V per cell) or NiMH (1.2V per cell).
To compare these, you need to use watt-hours instead to get a useful number.
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