Whenever you want to buy a powerbank for your phone, or battery, how do you know the capacity is falsified? After all dealing with fake products and returns can be a pain and at times costly as marketplaces only follow laws if exist. For example in eBay UK, I had to pay to return a fake phone and even then they got away not refunding me. In eBay US because of US laws, you do not need to return the item but provide evidence of its destruction if the item is fake which is far easier to do.
Due to the lack of proper laws, how can we protect ourselves when we shop online? Many places do not vet what they sell and the legalities surrounding the requirement to verify what you sell tends to be lacking. While fake phones are easy to spot if you have access to it on the spot and know what apps to use, batteries on the other hand are degradable items on use and testing them on the spot may not be possible, with verifying it taking time.
The best way to check if a battery is close to its rated capacity is with knowledge and understanding of both numbers and reviews. For example a customer may not be happy, but that customer could be right or wrong. Sometimes verifying requires prior knowledge on trends like the capacity range of mobile phone batteries and amps.
First you’ll need to understand what Ah or mAh is. Amp hours is the number of amps the battery can supply for an hour before it is fully discharged. If a battery rated 1Ah powers a device that pulls 1A constantly, that battery will be depleted in 1 hour.
2nd you need to understand watts and watt hours and the relationships. Watts = voltage x amps. Watthours = voltage x amp hours. It works the same. A battery of 10Wh if attached to a device that uses 10Watts will be fully drained in an hour. If it uses 1 watt constantly, then it’d take 10 hours to fully drain the battery. Watt hours is the true energy capacity of a battery. The reason we use hours is because watts is per second, so If we converted watt hours to watts (x60 twice) we get big numbers and devices typically consume a consistent number of watts or average but may not consume same amount of amps. This is because devices even people require a fixed amount of energy. By reducing the voltage we must draw more amps to compensate to get the same amount of energy. You can think of this in speed and gears for a car. If you decrease the gear, you increase the revs needed to maintain your speed, and since the energy required to maintain that speed is the same, barring increased friction from revs, the amount of fuel burnt in modern engines is the same. Batteries lose voltage as they lose charge and the nominal voltage helps us estimate just how much energy it has.
Let’s take a common battery, the USB powerbank. Its output is USB 5V and usually has either lithium ion or lithium polymer batteries that have a voltage of 3.7V. Let’s say the seller rates the battery at 10000mAh (10Ah), first we calculate the approximate watt hours 3.7V*10Ah=37Wh. Irregardless of interfaces, let’s say it has to be recharged via micro USB which a good cable would supply 2A. 2A via USB is 10Watts (2A*5V) but to fully charge it we must supply 10watts over 3.7 hours. So what we’ll want to find here are comments that the minimum recharge time for this product is 3.7 hours (or 4 hours). This isn’t just the stat you’ll need but its a helpful one which even you can test yourself when you obtain the product and charge it yourself from empty. Sometimes cables can be poorly made that’s why this number alone can’t be taken. If the cable has only 1A of capacity, and charges to full in the same amount of time then it only has half the rated capacity. If you don’t have a USB power Meter, usb2 ports are rated to output 0.5A unless the device/board states otherwise. USB charges that say 2A may not output 2A if the cable is of poor quality.
The next stat is to estimate battery drain for capacity. You’ll also find comments that say didn’t last a whole day or didn’t charge enough numbers of times. During heavy use, phones can use upwards of 10watts or more, which means this battery can be depleted in just 3 hours of heavy use. Given smartphone also use lithium and have the same voltages, its easy to estimate based on battery capacity ranges. If the battery is around 2.5Ah, the power bank would fully charge it 3+ times because as the phone is being charged, it is still on and using a bit of power which adds up over time when charging. Phone battery capacities are typically between 1-3Ah and it helps if the comment mentions the phone used as you can then look up its battery capacity on gsmarena.
However even with these numbers we cannot get an accurate estimate, only an approximation. Batteries can degrade in capacity over time, and this applies both to the device being charged and the battery itself if it has been in storage for a long time. This is why for lithium’s they typically come with around 40% charge as that’s a safe way to store them for longevity and why we have to charge them first before using. A lithium battery in storage for long fully charged degrades fast and can expand or explode. That is why if you plan to keep your lithium’s unused for a month to discharge them to 40%.
With other battery technologies it can get more complicated. Lead acids prefer to stay fully charged and do not like being discharged, hence has a significantly lower usable power than rated. Car batteries should not be drained below 80%. Other lead acid for APCs and backup power not below 50% while deep cycle can be drained to 20% before permanent damage occurs. That means a normal lead acid battery rated at 10Ah has a usable capacity of 5A as the voltage will drop faster too.
Its impossible to be certain with seller claims on capacity at first inspection, but understanding the numbers and general information can help significantly reduced getting scammed. Some power banks that offer other voltage outputs suffer higher drain from the voltage conversion circuits so are far less efficient. For instance if you have a power bank providing 3 different output voltages, you’re going to get a lot less capacity from the battery but not so much less. Like with flash drives, always test after you buy and check the return policy.