Reserve Capacity (RC)
What Is Reserve Capacity?
RC measures the number of minutes a fully charged battery at 27degC (80degF) can deliver 25 amps before voltage drops below 10.5V. RC simulates a real-world emergency: your alternator fails while driving at night. How long can the battery power your headlights, ignition, fuel pump, and ECU before the engine dies?
Test Method (SAE J537)
- Battery is fully charged and stabilized at 27degC +/- 2degC
- A constant 25A discharge is applied
- Voltage is monitored continuously
- Timer stops when voltage reaches 10.5V
- Result is recorded in minutes
A higher RC number means longer runtime without the alternator. For most passenger cars, 90-120 minutes is adequate. Vehicles with heavy electrical loads (aftermarket audio, winches, auxiliary lights, computer equipment) need 120+ minutes.
Typical RC Values by Vehicle Class
| Vehicle Class | Typical RC |
|---|---|
| Compact car (1.3-1.6L) | 60-90 min |
| Mid-size sedan (2.0-2.5L) | 90-120 min |
| Large sedan/SUV (3.0L+) | 120-150 min |
| Light truck/diesel | 150-180 min |
| Heavy-duty truck | 200-400 min |
RC and Battery Selection
RC is especially important for: - Emergency vehicles — must operate lights and radios without engine - Marine applications — bilge pumps, navigation lights during engine-off periods - Remote area vehicles — longer runtime if alternator fails far from service - Vehicles with aftermarket electronics — audio amplifiers, inverters, auxiliary lighting - Fleet vehicles with telematics — GPS trackers, cameras drawing constant power
Chengguang Heavy Duty RC
| Model | Estimated RC | Application |
|---|---|---|
| 145G51 | 200-250 min | Medium trucks, buses |
| 190H52 | 300-400 min | Heavy trucks, equipment |
RC values for SLI models are available in batch test reports. Request your order's RC data.
Author: Chengguang Power Tech Engineering Team | Reference: SAE J537