Mini FaQ
1. Manufacturers indicate the capacity of banks in accordance with the capacity of batteries installed in the device. This technique is generally accepted.
2. When assessing the capacity of a bank, losses must be taken into account. For example, for the most common use case of a bank for charging a device’s battery, the following losses occur:
- loss when converting from 3.7 V battery to 5 V output voltage in the bank;
- loss when converting from 5 V input voltage to 4.2 V charging voltage in the charged device;
- losses in the rechargeable battery.
Considering the efficiency of each section 0.9 we obtain the total efficiency of 0.9 * 0.9 * 0.9 = 0.73. This figure is approximate and depends on many reasons, in particular, the charge mode. The manufacturer does not specify this figure in principle - after all, 2 of the 3 stages are not underway, but in the load. And nowhere is it not stated that it is necessary to measure, taking into account the losses in the consumer - for example, if you connect the LED lamp to the panibribank - only the loss of conversion in 5 V, and, accordingly, the total efficiency will be 0.9, and even more.
3. Sometimes another value of capacity is written on the banks - capacity in terms of an output voltage of 5 V. Theoretically, this is more correct - after all, the device produces most often 5 V, but in practice it only causes confusion.
Firstly, because this figure is obtained by formal multiplication of the battery capacity by the voltage difference 3.7 / 5 = 0.74 without taking into account the efficiency, which can vary.
Secondly, the fact that the coefficient obtained is close to that obtained in Section 2 is nothing more than a coincidence, and the output voltage may not be 5 V ...
It is easier to explain with an example: Pipo and Cube tablets have batteries of the same capacity, but Cube charges from 5 V, and Pipo charges from 9 V (my bank gives 5, 9 and 12 volts).
So, when charging Pipo, the capacity of a bank must be multiplied by 3.7 / 9 = 0.41 and, accordingly, will the bank be enough for a smaller number of charges? No, 5 and 9 volts are just intermediate values, but energy is still described in item 2 - both at Cube and Pipo, the bank will provide the same number of charges (at Pipo, even slightly more - 9 V loss less)
4. All these figures are approximate - the parameters and conversion efficiency depend on the mode, and even when charging devices, the output capacity will be different depending on whether the tablet is charged with a 2A charge current or a phone with a 0.5A charge current. other devices - not the only use !!!
5. Unforgettable about the temperature mode of operation - from 0 to +40 РЎ0.
At low temperatures, even lower than 0 РЎ0, the battery self-discharge increases by several times, i.e. If you carry it in the cold in a bag, then at the most crucial moment you can get a discharged battery. Also, when cooled, the battery capacity and its life are very significantly reduced. If it is possible, do not freeze the battery !!!