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> when you're building something and you control all the variables, its easy to say the voltage is fixed No, my point is I don't control that variable. I can't

> when you're building something and you control all the variables, its easy to say the voltage is fixed No, my point is I don't control that variable. I can't get 14.4V microcontrollers, nor 6.5V batteries. Neither can you. I am obliged to power it with 3.280V/0.1-150mA regulated power from 4.2/3.7/2.8 max/typ/min aluminized pouches of wet wipes. Wattage figures therefore won't help me. USB-PD sure runs at 5/9/12/15/20V. Off of 3.7V li-ion cells, to charge 3.7V li-ion cells. So it's clear how many times more capacity a 20100mAh power bank battery has over 5000mAh phone battery, or a series 6-cell 18650 laptop battery pack(with nominal 2600mAh capacity per cell: 9x2600mAh of 3.7V equivalent capacity). > And circling around, you can't be certain how many hours my 10,000mAh battery pack will run a 10W load. 37Wh? 3.7 hours, _ish_. Give or take one full hour. I don't even know what capacity of an advertised 10000mAh battery at ~0.3C might be. Battery capacity depends on discharge current. And here again it's current, not discharge energy.

vel0city 3y ago
> 3.7 hours, _ish_. Give or take one full hour. So after assuming a value that's not even printed on it we're not even sure within +-25%. What a great unit of measure for battery storage. When if it was just rated in Wh we'd actually know. I'd much rather a battery say how many Wh its good for, its nominal voltage, and its peak amps. Its incredibly easy to reason how many watts a phone uses, a laptop uses, a game console uses, a TV uses, a car uses, a blender uses, a kettle uses, etc. Then its easy for me to know how long can this battery potentially run X.
- numpad0 3y ago
  > When if it was just rated in Wh we'd actually know. No. The capacity literally changes depending on how fast you draw. This is especially a problem on lead acids, so they often have couple "n-hour rate capacity" figures to make estimates for your particular use cases. It's less of a problem for li-ion, where C-rates(not coulomb but alphabet cee) is used to plan for cell counts, runtime, current limits and required wire thickness(because wire thickness depends on current, yet again, not total energy through it). It's a non-issue for dry cells because it's among equipment designer's responsibilities to account for. And that has little to do with Wh vs mAh. It'll be easier to guesstimate more precisely from mAh using experiences and implications, if anything.
  - vel0city 3y ago
    > So it's clear how many times more capacity a 20100mAh power bank battery has over 5000mAh phone battery We don't, because we don't know the pack's battery voltage nor do we know the phone's battery voltage. You're assuming they're both 3.7V, but its not listed so we don't actually know unless we tear it open. In fact, my phone is rated for 3.85V, if the pack was rated at like 3.6V or less that's a decent bit of difference. Over 20,000mAh with that voltage difference we're talking about a discrepancy of 5Wh, which for a device using about a watt means five hours of difference in run time from that tiny discrepancy. Which, as mentioned, would be a good bit closer to a realistic answer if it just listed it in Wh, because personally I don't care what its internal pack voltage is I just care about how long it'll keep my 1W device alive. And even then, theoretically this battery pack can charge my laptop as well, that laptop's battery is definitely not even close to the same voltage as that battery pack. So comparing Ah to Ah there is pretty meaningless. I've got a battery pack here rated for 5,000mAh. Roughly the same size as my phone, huh. Oh wait, its 56V. So roughly how many times can I charge my phone's battery off this pack? Going by Ah, once! But if I just knew my phone battery was ~17Wh, and we knew the battery was 280Wh, then we can guess we'll get about 16ish charges off of it. https://www.jackery.com/products/explorer-1000-portable-power-station?variant=40178306875479 https://www.jackery.com/products/explorer-1000-portable-powe... Would you honestly state for understanding the capacity of the above device it would be more useful if it gave some rating in purely Ah? We've got no info on its internal pack voltage, that's practically useless to us. Its input is 24V, but is that what its internal pack actually is? Who knows. Clearly 3.7, because that's what we'll assume every pack is! Then its running things at all kinds of voltages: 12V, probably half a dozen profiles of USB-PD, and 110V. I want to charge my car and I'd like to know how long it'll take. I'll do the back conversions to go away from the useful units here so we're talking just purely amps here, and its a 170Ah battery pack. I'll be pulling 40A from the wall. So roughly four and a quarter hours to charge, right? Nope, we didn't normalize for voltage. Well, we can normalize for voltage if we're just looking at watts. So its 240V 40A = 9,600W. Its a 68,000Wh battery pack. So the answer is a bit over 7 hours. And sure, you're absolutely right about c-rates. The total useful capacity of the battery is going to be different depending on the current you draw on it, fully agreed. But that same logic still applies if you're talking about runtime and you're doing your math purely in Ah. Running at half or double the amps doesn't necessarily mean you'll get twice or half the life, your unit of measure doesn't change that, so I don't get why you're bringing up concepts like wire thickness when discussing which is the better unit to measure battery capacity in a general sense. Sure, if we're talking purely about you building a circuit and wanting a battery matched to the circuit exactly, matching the voltage is useful. And when you actually do have voltage fixed, Ah becomes relevant. But in the real world, voltages are all over the place. You don't know what my battery pack here is rated for, you only have a guess its 3.7V. That assumed 3.7V is different from the 3.85 my phone's battery is rated for and is way off what my laptop is, so its not a straight 1 to 1 comparison.

vel0city 3y ago

> 3.7 hours, _ish_. Give or take one full hour. So after assuming a value that's not even printed on it we're not even sure within +-25%. What a great unit of measure for battery storage. When if it was just rated in Wh we'd actually know. I'd much rather a battery say how many Wh its good for, its nominal voltage, and its peak amps. Its incredibly easy to reason how many watts a phone uses, a laptop uses, a game console uses, a TV uses, a car uses, a blender uses, a kettle uses, etc. Then its easy for me to know how long can this battery potentially run X.

numpad0 3y ago
> When if it was just rated in Wh we'd actually know. No. The capacity literally changes depending on how fast you draw. This is especially a problem on lead acids, so they often have couple "n-hour rate capacity" figures to make estimates for your particular use cases. It's less of a problem for li-ion, where C-rates(not coulomb but alphabet cee) is used to plan for cell counts, runtime, current limits and required wire thickness(because wire thickness depends on current, yet again, not total energy through it). It's a non-issue for dry cells because it's among equipment designer's responsibilities to account for. And that has little to do with Wh vs mAh. It'll be easier to guesstimate more precisely from mAh using experiences and implications, if anything.
- vel0city 3y ago
  > So it's clear how many times more capacity a 20100mAh power bank battery has over 5000mAh phone battery We don't, because we don't know the pack's battery voltage nor do we know the phone's battery voltage. You're assuming they're both 3.7V, but its not listed so we don't actually know unless we tear it open. In fact, my phone is rated for 3.85V, if the pack was rated at like 3.6V or less that's a decent bit of difference. Over 20,000mAh with that voltage difference we're talking about a discrepancy of 5Wh, which for a device using about a watt means five hours of difference in run time from that tiny discrepancy. Which, as mentioned, would be a good bit closer to a realistic answer if it just listed it in Wh, because personally I don't care what its internal pack voltage is I just care about how long it'll keep my 1W device alive. And even then, theoretically this battery pack can charge my laptop as well, that laptop's battery is definitely not even close to the same voltage as that battery pack. So comparing Ah to Ah there is pretty meaningless. I've got a battery pack here rated for 5,000mAh. Roughly the same size as my phone, huh. Oh wait, its 56V. So roughly how many times can I charge my phone's battery off this pack? Going by Ah, once! But if I just knew my phone battery was ~17Wh, and we knew the battery was 280Wh, then we can guess we'll get about 16ish charges off of it. https://www.jackery.com/products/explorer-1000-portable-power-station?variant=40178306875479 https://www.jackery.com/products/explorer-1000-portable-powe... Would you honestly state for understanding the capacity of the above device it would be more useful if it gave some rating in purely Ah? We've got no info on its internal pack voltage, that's practically useless to us. Its input is 24V, but is that what its internal pack actually is? Who knows. Clearly 3.7, because that's what we'll assume every pack is! Then its running things at all kinds of voltages: 12V, probably half a dozen profiles of USB-PD, and 110V. I want to charge my car and I'd like to know how long it'll take. I'll do the back conversions to go away from the useful units here so we're talking just purely amps here, and its a 170Ah battery pack. I'll be pulling 40A from the wall. So roughly four and a quarter hours to charge, right? Nope, we didn't normalize for voltage. Well, we can normalize for voltage if we're just looking at watts. So its 240V 40A = 9,600W. Its a 68,000Wh battery pack. So the answer is a bit over 7 hours. And sure, you're absolutely right about c-rates. The total useful capacity of the battery is going to be different depending on the current you draw on it, fully agreed. But that same logic still applies if you're talking about runtime and you're doing your math purely in Ah. Running at half or double the amps doesn't necessarily mean you'll get twice or half the life, your unit of measure doesn't change that, so I don't get why you're bringing up concepts like wire thickness when discussing which is the better unit to measure battery capacity in a general sense. Sure, if we're talking purely about you building a circuit and wanting a battery matched to the circuit exactly, matching the voltage is useful. And when you actually do have voltage fixed, Ah becomes relevant. But in the real world, voltages are all over the place. You don't know what my battery pack here is rated for, you only have a guess its 3.7V. That assumed 3.7V is different from the 3.85 my phone's battery is rated for and is way off what my laptop is, so its not a straight 1 to 1 comparison.