How I Built a 119,000mAh DIY Power Bank from 34 18650 Batteries A Step-by-Step Guide

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How I Built a DIY 119,000mAh Power Bank Using 18650 Batteries from AliExpress
Detachable No Welding DIY 32*18650 Power Bank Case Battery Storage Box QC3.0 Quick Charge For iPhone Xiaomi Huawei Battery Shell (be sure to click on the one that has the wireless charging)
https://www.aliexpress.us/item/1005007260674584.html?gatewayAdapt=glo2usa

EVE 35V 18650 3500mAh 10A Battery ($2.50 Regular price$4.99)
https://www.18650batterystore.com/products/eve-35v-18650-3500mah-10a-battery

Timestamps:
0:00​ - Intro
1:59 - How I Built a DIY 119,000mAh Power Bank Using 18650 Batteries

As a digital nomad, having a reliable power source is essential, especially when traveling to remote locations or working on the go. While commercial power banks are convenient, they often lack the capacity and customization options needed for more demanding use cases. That’s why I decided to take matters into my own hands and build a DIY power bank with a massive 119,000mAh capacity (or 440Wh), using 18650 batteries purchased from AliExpress. Here’s how I did it.

Why Build a DIY Power Bank?

Before diving into the build process, let's talk about why I chose to build a power bank myself:

1. **Higher Capacity:** I wanted a power bank that could charge multiple devices, including my laptop, smartphone, tablet, and even a portable Wi-Fi router, multiple times without needing a recharge.
2. **Cost-Effective:** The cost of purchasing a commercial power bank with similar capacity would have been significantly higher than building one myself.
3. **Learning Experience:** Building a power bank from scratch was an exciting challenge that allowed me to expand my knowledge of electronics and battery technology.
4. **Customization:** I wanted to create a power bank with specific features, such as multiple USB ports, a fast-charging option, and an on/off switch.

The Components I Used

To build my DIY power bank, I needed the following components:

- **34 x 18650 Batteries (3500mAh each):** I purchased these from AliExpress. Each battery has a capacity of 3500mAh, and together, they provided a total of 119,000mAh (34 x 3500mAh).
- **Battery Management System (BMS):** To manage the charging and discharging of the batteries and provide protection against overcharging, over-discharging, and short circuits.
- **Spot Welder:** For securely connecting the batteries in a safe and efficient manner.
- **Boost Converter Module:** To step up the voltage from the batteries to the required output level (typically 5V or higher for USB charging).
- **USB Charging Module:** For charging multiple devices simultaneously. I opted for a module with multiple USB-A and USB-C ports to support various devices.
- **Heat Shrink Tubing and Electrical Tape:** For insulation and securing connections.
- **Wires and Nickel Strips:** For connecting the batteries in series and parallel configurations.
- **Enclosure Box:** A sturdy and heat-resistant box to house all the components safely.
- **Multimeter:** For checking voltages and ensuring all connections are correct.

Step-by-Step Build Process

Step 1: Plan the Battery Configuration

To achieve the desired capacity and voltage, I needed to configure the batteries properly. Since I used 34 batteries with a capacity of 3500mAh each, I decided to connect them in a combination of parallel and series to maintain a manageable size and ensure adequate voltage output.

I arranged the 34 batteries in a configuration of 17 parallel sets of 2 batteries each (17P2S). This provided a total capacity of 119,000mAh at a nominal voltage of 7.4V (2 sets of 3.7V each in series).

Step 2: Spot Weld the Batteries

Using a spot welder, I securely welded the batteries together with nickel strips. Spot welding is the preferred method for connecting 18650 batteries as it provides a strong and reliable connection without generating excessive heat that could damage the batteries.

I carefully aligned the batteries and welded the positive terminals of one set to the negative terminals of the adjacent set in parallel, ensuring a secure connection. I then connected each parallel set in series to achieve the desired voltage and capacity.

Step 3: Install the Battery Management System (BMS)

The BMS is a crucial component that ensures the safety and longevity of the power bank. It balances the charge across all cells and protects the batteries from overcharging, over-discharging, and short circuits.

I connected the BMS to the battery pack according to the manufacturer’s instructions. This involved connecting the BMS’s input terminals to the positive and negative terminals of the battery pack and the output terminals to the boost converter.

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