Low-cost DIY Power Bank With Replaceable Batteries Using Lithium Batteries

This low-cost DIY power bank is only for transitional use, and it can just make use of the extra lithium batteries and provide some experience. For long-term use or long-term outdoor activities, it is recommended that you use a power bank from a big brand, which is safe and guaranteed.

A power bank is nothing more than a battery cell, a charging module, and a discharging module. If the battery is replaceable, the charging module can be omitted, and a boost module can be directly added to the battery cell.

1. 18650/21700 battery cell and battery box
2. Integrated charge and discharge power management module
3. Dental floss box
4. Wires
5. Tape
6. Soldering iron

There are only two interfaces on the whole motherboard, which can be welded on both sides. Just connect the + to the positive pole of the battery cell and the - to the negative pole of the battery cell. In order to replace the battery, I connected a battery box. I connected several boxes in parallel to the number of cells I want to put in. After the wires are connected, put in the lithium battery and you can charge the phone.

When charging, the phone is tested for charging, and the charger voltage is about 4.6V, the maximum current is 1500ma, and the stable current is about 1000ma. The specific output current is related to the charging protection of the phone and the power of the phone.

When charging the phone, the overall heat is also a bit high. The fingers can feel hot when touching the components. The inductor component and the USB interface are the hottest, but the battery is basically not hot, so it is still okay. I don't know if the battery is too bad. It will show full soon when charging. After it shows full, it actually takes a long time to charge the charger before it is really full.

During the process, one of the batteries was installed upside down, causing a short circuit between the positive and negative poles, and sparks flew instantly. Then the battery was quickly taken out. It was a little hot, but not serious. Fortunately, the battery and the power board were not damaged. The wires and tape were burnt. Later they were re-welded and made smaller so that it could fit into the dental floss box, and then glued down later.

If you want to DIY and don't have extra batteries, it is recommended to buy better 21700 batteries. They are not much bigger but have higher capacity. It is also recommended to buy lithium batteries from big brands or stores with good reputations.

Due to limited tools, the charging and discharging voltage, current and conversion rate of the entire circuit cannot be accurately measured, but the overall use is feasible. Replacing a better power battery and using soldering for all purposes will probably produce better results. The above is just a personal DIY solution. There is no temperature control, no fast charging, and it is unsafe, but it can make use of idle lithium batteries and the size can be very small. It is still possible to occasionally charge wireless headphones, bracelets, flashlights, and LED devices.