Project RePack: Build Your Own Modular & Repairable 11.1V Li-ion Battery Pack

 Introduction

Most 11.1V battery packs are made by permanently welding together 3 Li-ion cells. While this works for compact builds, it's a huge limitation when one cell fails — you have to throw away the entire pack or go through a risky and complex repair.

That's why I created Project RePack — a modular, removable battery pack system that allows you to safely replace individual cells, charge them using a balance charger like the iMAX B6 V2, and easily integrate it into your DIY or robotic projects.

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Components Required

• 🔋 3x 18650 Li-ion cells (3.7V each, same capacity recommended)

• 🔲 3-slot 18650 battery holder case (with series configuration)

• 🔌 Jumper wires (male/female)

• 🔘 Toggle or slide switch

• 📦 XT60 / JST connector (optional for clean connections)

• 🔧 Soldering tools (only for wires and switch, not the cells)

• 🔋 iMAX B6 V2 Balance Charger

• 🔒 Heat shrink tubing, insulation tape

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Assembly Steps

1. Insert the Batteries

• Place the 3 Li-ion cells into the 3-slot holder in series (total output: 11.1V nominal).

• Ensure the battery holder supports series output (positive of cell 1 to negative of cell 2, and so on).

2. Connect the Output Wires

• Solder jumper wires from the positive and negative terminals of the holder to an external connector or directly to your project.

• You can use an XT60 or JST connector for clean, swappable connections.

3. Add a Switch

• Wire a toggle switch in-line with the positive wire to allow power control.

• This helps you turn off the battery output safely .

4. Balance Charging Wires

• Add thin wires to each cell tap point for balance charging:

  • Red wire(4) - Positive terminal of the battery holder

  • Black wire(3) - Connect on the Cell 2+

  • Black wire(2) - Connect on the Cell 3+

  • Black wire(1) - GND of the battery holder

• Connect these wires to a balance connector compatible with iMAX B6 for safe charging/discharging.

⚠️ Important: Only use the iMAX B6 charger in Li-ion 3S balance mode to prevent overcharging or thermal runaway.

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How It Works

• The battery pack delivers 11.1V (3.7V × 3) and can be recharged safely using the iMAX B6 V2 in 3S mode.

• When one cell is degraded, simply remove and replace it — no soldering or destructive disassembly needed.

• The switch and jumper wires make it project-ready — just plug and play.

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Photos & Diagrams

• Diagram of wiring layout

Soldering in the battery holder

• Image of installed battery holder

                                        

after a little bit of wire management,

• Charging setup with iMAX B6

        Check the battery's are connected properly and are not dead cells by going into the tool kits.

After checking this, it is good to charge the battery. 

After selecting the values, Long press the 'Enter' button to Charge

Press Enter.

After Charging,

If any issues check the wiring and for connectivity issues like loose contact, some surface will not be conductive.

You can use a multimeter to check the connectivity or make a simple circuit and check it out.

• Final connected project

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Advantages Over Traditional Packs

• 🔁 Repairable — replace cells instead of full packs

• 🛡️ Safe charging — with balance leads and verified charger

• 🔌 Plug-and-play — jumper wires make it project-ready

• ♻️ Eco-friendly — fewer discarded battery packs

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Final Thoughts

By making battery packs modular, we extend the life of our electronics, reduce waste, and improve safety. This project is ideal for robotics, drones, or portable systems where power flexibility is key.