Battery Science for Robotics
Your battery is your fuel tank. Learn about internal resistance, voltage sag, and why you should never charge at 4A.
Battery Science for Robotics
Crucial Match 1: Your robot slows down. Crucial Match 2: Your robot disconnects. Is it code? Is it the field? No. It’s your battery.
The Chemistry
FTC uses 12V NiMH batteries. They are old technology. They are heavy. And they are temperamental.
Voltage Sag
When your motors draw current (e.g., accelerating fast), the battery voltage drops.
- Rest: 13.5V
- Accelerating: 11.0V (Good).
- Bad Battery: 8.0V (Critical).
If voltage drops below ~7V, your Control Hub reboots. Game Over.
Charging Best Practices
- The Golden Rule: Charge at 0.9A or 1.0A. Never faster.
- Fast charging (2A-4A) creates heat. Heat destroys the battery’s ability to hold voltage under load.
- The “False Peak”: Chargers often stop early. Feel the battery. If it’s cold, it’s not done. If it’s warm, it’s done.
Internal Resistance
Old batteries develop high Internal Resistance. This means they look “Charged” (13V), but the moment you drive, they die. Test your batteries: Use a Battery Beak or load tester. Throw away bad batteries. Do not use them for practice.
Conclusion
Mark your batteries. Track their age. A $50 battery is cheaper than losing a World Championship match.