Yes.
Lithium batteries can be placed in metal iron boxes, but be careful not to let the electrodes touch the box at the same time to avoid short circuits.
There are dangers. The main one is that battery self-discharge will cause battery power failure. The iron box will cause the positive and negative poles of the battery to be connected, causing shock. short circuit between poles, causing the battery to overheat and explode, so you need to be careful.
It's very embarrassing. Almost all mobile power cells have the same properties as charging batteries, which are 3.7V lithium batteries. If you want to DIY, you must first have a charger to charge your 20V battery . Then you need to use a step-down circuit to reduce the battery voltage from 20V to 5V and limit the current to less than 2000mA beforecharge the lithium. . Battery charging, of course, you need to be able to charge your cell phone, and you definitely want to use it as a mobile power supply, so you need to have a suitably sized, easy to deal with case to accommodate your battery and. Step-down current limiting circuit, and on the box open holes of suitable size and shape to safely install the USB output jack and Micro or DC input jack for charging 20V battery as charging interface , and install a movable power switch on the box. There are almost no off-the-shelf circuits to reduce the voltage and current limit of a 20V3A battery to 5V2A. You need to have basic circuit knowledge and buy a bunch of components to deal with them yourself. You will need to personalize them. Waiting for all of this is time consuming, laborious and expensive. After finishing it reluctantlySister, you will find that you have spent so much money and energy to build something indescribable, even ugly, and you will regret it. It's best to buy a brand new Xiaomi 10400mAh power bank in your 60s, even if your spirit of exploration is commendable.