If your laptop/notebook or netbook has been changed the battery unit with the new one. don't waste the old battery unit although it doesn't work anymore. Because generally inside the battery unit, not all the battery cell are bad. even in more case, in the battery unit that has 6 battery cells only one or two battery cells have malfunction. One cell has a problem, it will cause the battery unit becomes malfunction.
Take out all the batteries, generally has model 18650 battery, be care full don't make short circuit.
(You can buy 18650 battery charger from online market, from Aliexpress the price below 2 dollars)
There are many Powerbanks in the market have real capacity not the same as they write in the specifications, the real is below what they wrote.
You can build your own Power Bank with best capacity using old battery from your laptop, because original battery from laptop has best quality.
You must have the Power Bank case, you can buy from anywhere. In the Aliexpress store there are many model of Power bank casing for sale, buy the case for the 18650 battery model. with 5 or 6 batteries. The price is not expensive.
|Example Power Bank with 6 batteries|
See the polarity positive and negative, don't make a mistake. In all Electronic devices using the battery, the battery terminal with 'spring' is negative.
If it has problem in charging or problem when in use: Open the cover, take out the batteries, and measure the voltage of each battery using Volt meter, If found the battery much lower compared with other battery means that battery is damaged.