🔋 Mobility Scooter Battery Capacity Tester

A specialized diagnostic tool designed to measure the real-world health of Lead-Acid (AGM) batteries. It uses a simulated 5A load and automated ATmega328P ADC logging to determine the true discharge curve without damaging the cells.

Critical Threshold: Lead-acid batteries suffer irreversible damage if discharged below 30%. This system automatically disconnects the load at the 50% "Safe Limit" (12.23V) via a relay-driven Low Voltage Disconnect (LVD).

Downloads

Full Build Instructions and Project downloads on GitHub

How It Works: Smart Diagnostic Logic

To accurately simulate a mobility scooter in motion, the device uses a 110W resistive load (dual 12V-55W halogen bulbs). The system uses the following logic to ensure data accuracy:

Smart Voltage Checking: To get a true reading of how much "fuel" is left in the battery, the machine has to pause. It briefly turns off the power-draw every minute to take a "Resting Voltage" measurement. This is much more accurate than measuring while the motor is running, which can make a battery look emptier than it actually is.
Dual-Battery Monitoring: Most mobility scooters use two 12V batteries linked together to create 24V. Instead of just guessing the total health, the machine’s brain measures the first battery and the total power at the same time. It then does a quick bit of math ($$V_2 = V_{total} - V_1$$) to figure out exactly how the second battery is performing.
Heat Control: Running a 5-Amp test creates a lot of heat—similar to a bright car headlight. To keep things safe, the test bulbs are kept in protective glass cases and cooled by a high-speed fan to make sure the equipment stays cool and the results stay reliable.

Technical Specifications

Metric	Technical Value / Specification
Microcontroller	Arduino Nano (8-bit RISC @ 16MHz)
Discharge Load	5A Average (Dual 12V-55W Halogen Resistive)
Safety Cut-off	12.23V (Determined by 50% SoC Threshold)
Data Logging	SD Card (.CSV format) via SPI (MISO/MOSI)
Input Fusing	Triple 10A In-line Fuses for Cell Protection

Rugged Power Handling

Designed to handle the 21A peak currents measured during real-world grass riding. The 5A test load provides a highly accurate average-use simulation for Amp-Hour (Ah) calculation.

Accurate Health Check

While standard CCA (Cold Cranking Amp) testers give a "snapshot" of internal resistance, this device measures actual usable capacity over a full 5-6 hour discharge window.

Voltage-to-Capacity Reference

The system is programmed with the following reference values for 12V Lead-Acid batteries to ensure precise logging:

100% (Full): 12.89V
50% (Safe Limit): 12.23V
30% (Damage Risk): 11.96V
0% (Dead): 11.63V