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In USA, I always see portable batteries for mobile phone stating they have 5000 mAh, 10000 mAh, or 13000 mAh, etc. (One of the popular one is Anker as on Amazon.com). However, in Asia, I saw the batteries having a spec of 10000 mAh "battery capacity", but a "nameplate capacity" of 6200 mAh. Another battery was 10000 mAh but its "nameplate capacity" was 5100 mAh.

The word for "nameplate capacity" is "額定容量" and it seemed to mean "effective capacity". It seemed 10000 mAh is relative to 3.6V of the internal batteries in the charger, and the effective capacity is relative to 5V. (and if it is for QC 2.0 or 3.0 and 9V charging, then the mAh drops to close to about half).

How can we understand this? Does that mean batteries like Anker stating 10000 mAh is also nominal and it really has an effective capacity that is not stated?

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closed as off-topic by Nick Alexeev Feb 18 at 21:38

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    \$\begingroup\$ Ampere-hour is only a partial specification of battery capacity - you should also specify the battery voltage to get the real capacity. \$\endgroup\$ – Peter Bennett Feb 18 at 20:48
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Quite simply - they are lying to you, and including the "nameplate capacity" so that they can try to cover themselves.

Batteries are typically rated at 1C discharge - this means at a current level that will discharge the battery to the minimum safe level within 1 hour. So a 10Ah battery will discharge at 10A for 1 hour. If the nominal voltage was 3.7V, we can ballpark by saying that's 37Wh.

You can get maybe +5% by discharging a battery at a lower current - so for example 2A will probably get you 38.5Wh because there's less loss due to internal resistance (remember higher current = more lost due to resistance).

But you're not going to take a 6Ah battery and turn it into a 10Ah battery by using it differently.

I expect if you take any of these battery packs and run your own tests, you'll see. They rely on people not knowing any better and just buying something because it says that it's higher capacity.

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  • \$\begingroup\$ "1C" means 1 coulomb? So are you essentially saying that most (or maybe all) the batteries out there are stating 10000 mAh but effectively it only can give out about 6000 mAh? But I found the mAh quite misleading because the spec at the back of the box says at 9V, it is 3000 mAh, for example... and so I thought, maybe mAh is not that great for "capacity"... it is the capacity at a certain voltage. Maybe a better spec for these battery units is "36Wh" or if they want, "36000 mWh" or use joule. \$\endgroup\$ – 太極者無極而生 Feb 18 at 17:11
  • \$\begingroup\$ Respectable manufacturers will list both the mAh and Wh capacities of the battery. \$\endgroup\$ – vini_i Feb 18 at 19:09
  • \$\begingroup\$ @太極者無極而生: No, 1C is a measure of charge/discharge current relative to battery capacity. 6.2A is 1C for a 6.2Ah battery ("full charge" in 1 hour). \$\endgroup\$ – Peter Cordes Feb 18 at 20:28
  • \$\begingroup\$ @太極者無極而生 - "1C" in this context does NOT mean "One Coulomb." It refers to the "C-rate", where "C" is short for either "Current" or "Capacity." 1C is the current necessary to discharge the battery in 1 hour. At 0.5C, you are drawing current to discharge the battery in 2 hours --- note that this is not the same as "half the current at 1C". This is actually covered in a separate question here on EE Stack Exchange... electronics.stackexchange.com/questions/108114/… \$\endgroup\$ – Forbin Feb 18 at 20:29
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    \$\begingroup\$ I don't think this is true. The other answers are much more compelling, and I'm not sure why this one is upvoted so much. Here's a newspaper article that seems to explain that it means exactly what the other answers are saying (chinatimes.com/newspapers/20130822000282-260210) \$\endgroup\$ – BeB00 Feb 18 at 21:42
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This is because the amp-hour ratings of these packs are a bit ambiguous.

This type of battery pack has one or more internal cells along with a DC to DC converter. The cells generally have an operating voltage of somewhere between 2.8 and 4.2 volts, depending on the state of charge. Usually the 'nominal' voltage is around 3.7 volts. The internal cells are then connected to the USB connector via a DC to DC converter, which (relatively) efficiently converts the cell voltage to 5 volts.

However, because of the converter, the current drawn from the pack differs from the current drawn from the cells inside the pack. For example, if you draw 1A from the pack at 5V and your pack has one 3.7V cell, the cell will have to supply at least 1 A * 5 V / 3.7 V = 1.35 A. Also, the converter will not be 100% efficient, generally only 80-90%, so the cell current would probably be more like 1.35 / 0.9 = 1.5 A. This is where the rating becomes ambiguous: are the 'amps' in 'amp-hours' measured at the cell or at the USB port on the pack? Marketing dictates that the larger the number they put on the box, the more packs they will sell, so these numbers usually indicate the amp-hour rating of the internal cells, which IMHO is rather useless and misleading.

If you take your 10000 mAh / 6200 mAh battery as an example and assume a 3.7 V internal battery and a converter with 85% efficiency, 10000 * 3.7/5 * 0.85 = 6290 mAh, which is pretty close to 6200 mAh.

A much more useful method would be to specify the capacity in watt-hours or joules, which is independent of the voltage. But this would make far too much sense.

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  • \$\begingroup\$ you said "But this would make far too much sense" at the end... is that some kind of humor about how could business / commercial advertisement or marketing information make too much sense? \$\endgroup\$ – 太極者無極而生 Feb 20 at 8:45
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USB powerbanks typically consist of a single cell lithium battery (or for higher capcities multiple parallel cells). This has a voltage of 3-4V depending on it's state of charge. To get 5V for powering a phone it has to be run through a boost coverter which increases the voltage at the expense of current. It also has losses.

As such as you surmise in the question the capacity in AH measured at the cell is significantly higher than the capacity measured in AH at the output of the powerbank. Also cell manufactures AH claims are often to put it politely "optimistic".

My understading is that powerbanks marketed in the west are normally marketed based on cell capacity, not effective capacity.

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  • \$\begingroup\$ OK, this answer makes at least some sense, especially with the mention of boost converter so +1 that. So in other words, the high rating is in a sense "real", just highly optimistic about the battery itself, rather than what output at the port would be \$\endgroup\$ – Sergiy Kolodyazhnyy Feb 18 at 20:48

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