Power charger is common to many people nowadays, and now many power banks usually have the capacity of 5000mAh, 8000mAh or 10000mAh, it sounds really good.
Especially in the last two years, power charger looks more and more beautiful, the capacity is greater than before, but the old problem is still there - why the power cannot support to charge for a few times?
In fact, any power charger has a conversion rate. The upper limit voltage of the lithium battery is 4.2V (generally 3.7V), and the charging voltage can only be charged from high voltage to low voltage. No matter what kind of lithium battery the power bank use, only if it boost to 5V, can it charge for the phone, tablet PCs. There will be 10% to 20% of the capacity lost at the process of lithium battery boosting from 4.2V (3.7V) to 5V.
In general, assuming that there is no loss, the output capacity = (battery voltage × battery capacity) × conversion rate ÷ output voltage.
But the above assumption is the situation that has no loss of capacity in the process of charging. Now assume that your power charger have the conversion rate of 92%. According to the output capacity = (battery voltage × battery capacity) × conversion rate ÷ output voltage, actually a power bank with the capacity of 10000mAh, in the case that the conversion rate is 92%, the real output power is less than 7000mAh. However, currently a power charger with the conversion rate of 90% can be considered as very high quality ones. The truth is that in the current portable power bank market, there are almost no battery chargers having such a high conversion rate. Generally the power bank would have a conversion rate of around 60%-70%. Therefore, the real output power of the smartphone charger are far lower than 7000mAH.
In addition, the above results have not taken into account the effect of the surrounding circuit, cable and other aspects. These factors would also consume part of the power. Do you understand now? We cannot truly believe in the declared capacity of the power charger, as it is not the exact power that could charge into our phones or other electric devices.
So, do not consider 10000mAh as 10000mAh at all, the best situation would be consider 70% of the declared capacity. Not to mention those power charger with the conversion rate of about 50%.
Take WST DP512 power charger from Shenzhen Wanshuntong Science & Technology CO., Ltd as an example. This product has the conversion rate of 65% or so. This is the real statistics and it has been around the top statistics in the area. Many other power bank distributors’ products cannot reach this conversion rate at all.