TL;DR – BatteryDelete for SwitchBot Smart Lock

Replace the 4×AA batteries in your SwitchBot lock with two 5.5V 10F supercapacitors → no more battery swaps, consistent motor power, and reliable unlocks even during heavy use or outages.

Charges in <1 minute with a 6v power supply
Holds ~24 hours of typical usage when fully charged (emergency/offline mode)
Fits inside the original battery enclosure (3D-printed custom part)
Full open-source files: KiCad schematics/PCB + FreeCAD enclosure/STLs
Buy pre-assembled kit for $50 (skip soldering, fab waits, and assembly): Order here →

Tested at home for over a year – solves the common “dead batteries lock you out” problem.

BatteryDelete for SwitchBot: An Open-Source Supercapacitor Upgrade

Ditch the AA Batteries with a Supercapacitor Solution

Did your smart lock batteries die and you had to drive 8 hours to let your guests in? Mine did – and that’s why I created BatteryDelete for my SwitchBot smart lock.

SwitchBot smart locks use 4×AA batteries which often drain quickly (2-3 weeks) leading to premature failures. Weak batteries degrade power to the motor, resulting in failed unlocks and potential security issues (e.g. door left unlocked when you’re away, getting locked out). The frequent trips to service the lock at unexpected times is a source of pain and a major reliability issue. Can’t set-and-forget!

I designed the BatteryDelete module to power the SwitchBot consistently and eliminate battery swaps. I have been testing it for reliability at home for over a year with excellent results.

It mechanically replaces the original W-shaped battery enclosure seamlessly and powers the SwitchBot with a consistent voltage × current curve that batteries fail to deliver when they drop below 75% capacity.

Open Source Approach

I believe in the maker community’s principle of sharing knowledge. That’s why I’m releasing the complete BatteryDelete design as open source:

For DIYers: Free 3D models, schematics, and PCB files on GitHub to build your own
For convenience: Pre-assembled, tested modules available for $50 if you’d prefer a ready-to-install solution

Whether you build it or buy it, you’re getting the same reliable design I’ve been using daily for over a year. My hope is that sharing this work helps the SwitchBot community while also connecting with fellow embedded developers and makers.

All revenue from sales goes back into funding more open-source hardware projects for the smart home community.

Why Supercapacitors Instead of Batteries?

Supercapacitors offer significant advantages over traditional batteries:

Fast charging: Full charge in under a minute
Longevity: Millions of charge cycles vs. batteries’ thousands
Consistent power delivery: Provide burst power for the motor without degradation
Reliable operation: With normal usage, they charge to 3.1V and maintain that level throughout their lifetime
Power outage resilience: Stay functional for many hours during outages

Project Overview

This project combines mechanical design, electronics engineering, and manufacturing. I used open-source software packages and was pleasantly surprised by how mature they had become.

The Electronics Design

BatteryDelete Schematics for SwitchBot smart lock — Figure 1) Schematics of the BatteryDelete module

Component Selection and Design Rationale

The supercapacitors (10F, 5.5V) are designed to operate at approximately 50% of their maximum voltage rating for better longevity through their millions of rated charge/discharge cycles.

Super Caps — Figure 2) Super Capacitor 5.5V 10F 13x26x27mm

Protection Circuitry

Schottky diode (D1): Grounds any backward current surges into the power supply
Slow-blow fuse (F1): Protects the circuit against power supply over-current surges
Current limiting resistor (R1): The 2W/5Ω resistor limits the maximum charge current to 3A when the capacitors are fully discharged during the initial (1xRC) stage of the charging curve (approximately 10 microseconds)

ChargeCurve — Figure 3) C1 and C2 supercaps charging curve

Zener diodes (D2 and D3): 5.1V Zener diodes offer additional overvoltage protection
Balancing resistors: R2 and R3 resistors ensure even charge distribution across the modules
TVS diode (D4): Suppresses any spurious motor transient currents to ground at the output

Voltage Safety

With 6.5V input, the series stack charged to 6.2V total in under a minute (~3.1V average per 5.5V-rated 10F module). This is only ~56% of each module’s maximum rating, well within safe margins for these winding-type supercapacitors (which internally use two ~2.7–3.0V cells in series with factory balancing). No heat, excessive current, or degradation signs were observed.

For maximum lifespan of C1 and C2 (where the module may hold charge for weeks), the final design targets ≤3.5V charging per capacitor—still providing ample energy for reliable motor operation while minimizing any long-term stress.

PCB Design Process

Thanks to KiCad library’s vast collection of components and footprints, I quickly drew the schematics. I then sourced most of the parts from Amazon, applied the footprints, and designed the PCB in KiCad PCB Editor.

I initially tried to use the FreeRouting plugin for KiCad, but it didn’t work. To work around this, I imported the KiCad schematics into Fusion 360 and used the Fusion autorouter, which worked brilliantly. However, I quickly realized the one-way import of the schematics from KiCad into Fusion proved painful when modifications were needed.

Eventually, I gave up on using Fusion’s autorouter and moved the design back to KiCad PCB Editor. Manually routing the tracks worked well because I overrode the default autorouting settings and added more copper to the wider PCB tracks. I moved the GND to the bottom layer for better thermal relief, even though I detected zero overheating during operation of the prototype I built for testing.

The Mechanical Design

Figure 4) The 3D model of the BatteryDelete enclosure

The supercapacitors aren’t small: 13×26×27mm. I designed the W-shaped mechanical enclosure to accommodate them in FreeCAD v1.0.2 and then designed two PCBs to fit the capacitors, one in each lobe of the W-shaped battery enclosure.

The power supply attaches to the enclosure using two connector plates where it’s marked with a + sign. The other side with two pin-holes has connector plates to power the SwitchBot.

Software and Packages Used

Electronics Design

KiCad v9 schematics editor
Fusion 360 PCB design and autorouter (initially)
KiCad v9 PCB Editor (final)

Parametric 3D Modeling and 3D Printing

FreeCAD v1.0.2
OrcaSlicer
Prusa MK4

PCB Fabrication

OSH Park

The Manufacturing

Figure 5) BatteryDelete PCB and 3D assembly view

PCB Fabrication

The quotes for PCB manufacturing from local and overseas fabrication houses ranged astronomically from $8.60 for 3 prototypes to $1,000 for 5-100 prototypes! Needless to say, I went with the $8.60 option even though I had to wait 3 weeks to get them back from the fab house. The $991.40 savings was well worth the wait. I also tried using a CNC milling machine for quick prototyping of the 2-layer PCBs—a story for another day!

3D Printing

I built the enclosure on a Prusa MK4 3D printer with a 0.4mm nozzle using PETG filaments for their rigidity and durability. The results were better than expected even without using any support infills. I had another model built with PLA which looked somewhat smoother because of the softer plastic, but I opted for PETG for its better thermal characteristics.

Installation Guide

⚠️ Safety Notice: This modification may void your SwitchBot warranty. Ensure you understand basic electronics and are comfortable with minor hardware modifications before attempting installation. Never connect standard AA batteries to the modified charging terminal.

Installation Steps

Open the fiberglass back panel of the SwitchBot (2 Phillips screws)
Drill an M3 hole in the middle of the panel and route the power supply cable through it
Disconnect the white cable from the battery plate on the left and connect the positive power supply line to it (the +6.2V supply line)
Connect the negative power supply line to the ground battery plate (the common middle plate)
Put back the SwitchBot panel using the same 2 Phillips screws
Mount the SwitchBot on your door as before—this will hide and secure the power supply wire between the lock and the door

How It Works

Inserting the BatteryDelete module inside the smart lock will charge the supercapacitors to operational voltage within a few seconds, and the smart lock will be powered from the BatteryDelete module just like it was powered from batteries before.

By disconnecting the white cable (in step 3) and replacing it with the +6.2V supply line, we created a charging terminal for the BatteryDelete module. Remember to never connect batteries to this terminal because the terminal is powered by the power supply. We call this lobe of the battery enclosure the “input lobe.”

The other lobe of the battery enclosure, the “output lobe,” powers the smart lock via the supercapacitors.

You could also insert the original AA batteries as per the original design. Note that the original 4×AA battery enclosure only ha connectors on the output side ( not where the + sign is), this is why it is safe to insert the orginal enclosure with 4xAA batteris if you decide not to use the supercapacitors for any reason, and the smart lock will function normally as designed with 4×AA batteries.

Performance Results

After 12 months of daily use:

Zero degradation of supercapacitors observed
Flawless operation through 15+ power outages
Consistent voltage maintained at designed 5.1V level
No thermal issues during normal operation
Instant recovery after power outages (sub-minute recharge time)

Getting Started

Option 1: Build It Yourself (Free)

What you’ll need:

3D printer (0.4mm nozzle, PETG recommended)
PCB fabrication service (~$9 for 3 boards from OSH Park)
Components from BOM (~$12 from Amazon/Digikey)
Basic soldering skills
Power supply (> 6.2V DC adapter)

Download: GitHub Repository

Time investment: 2-3 hours assembly + waiting for PCB fabrication (typically 2-3 weeks)

Total cost: ~$15-20 in parts if you have access to a 3D printer and PCB fabrication

Option 2: Pre-Assembled Module ($50)

What’s included:

Fully assembled BatteryDelete module
Quality tested (24-hour charge/discharge cycle verified)
Installation guide
Email support

Order: www.entriom.com

Ships in: 3-5 business days

Why Offer Both Free Files and Assembled Units?

I’m sharing this design freely because the maker community has given me so much through open-source projects over the years. At the same time, I recognize not everyone has:

A 3D printer and PETG filament
Access to PCB fabrication services
Soldering equipment and skills
Time to source 15+ components from various suppliers

The $50 assembled option covers my material costs, fabrication time, quality testing, and allows me to continue developing open-source solutions like this. Think of it as supporting the project while getting a tested, ready-to-use product.

Contributing to the Project

This is an open-source project and I welcome improvements! If you:

Build one and find issues
Have ideas for v2.0 features
Want to port this to other smart locks
Discover optimization opportunities

Please open an issue or pull request on GitHub. I’m excited to learn from the community and collaborate on making this even better.

Open-Source Design Files

All project files are available in this dedicated GitHub repository:

github.com/EmeelNoohi/entriom-switchbot-batterydelete

KiCad schematics & PCB layout
FreeCAD parametric enclosure model (.fcstd)
Exported STL files for 3D printing
Prusa MK4 g-code file
Gerber files

Fork the repo, build your own, suggest improvements, or open issues/PRs. Questions? Feel free to comment below or open an issue on GitHub.

License: MIT

Future Expansion

Alternative non-invasive charging methods are being explored for future versions to make installation even simpler.

About the Developer

I’m Emeel Noohi, a firmware developer specializing in embedded systems, smart home automation, and IoT devices. This project combines my passion for solving real-world problems with robust engineering solutions. Check out my other work at www.entriom.com, including g.io—a hands-free keyless gate entry system.

Connect: LinkedIn | GitHub