Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Charging Time Required
The time required to charge a battery will vary, depending upon the following factors:
- Battery Capacity - A completely discharged heavy-duty battery requires twice the charging time of a small capacity battery.
- Temperature - A longer time will be needed to charge a battery at -18° C (0° F) than at 27° C (80° F). When a fast battery charger is connected to a cold battery, the current accepted by the battery will be very low at first. As the battery warms, it will accept a higher charging current rate (amperage).
- Charger Capacity - A battery charger that supplies only five amperes will require a longer charging time. A battery charger that supplies twenty amperes or more will require a shorter charging time.
- State-Of-Charge - A completely discharged battery requires more charging time than a partially discharged battery. Electrolyte is nearly pure water in a completely discharged battery. At first, the charging current (amperage) will be low. As the battery charges, the specific gravity of the electrolyte will gradually rise.
The Battery Charging Time Table gives an indication of the time required to charge a typical battery at room temperature based upon the battery state-of-charge and the charger capacity.
| BATTERY CHARGING TIME TABLE | |||
|---|---|---|---|
| Charging Amperage | 5 Amps | 10 Amps | 20 Amps |
| Open Circuit Voltage | Hours Charging @ 21° C (70° F) | ||
| 12.25 to 12.49 | 6 hours | 3 hours | 1.5 hours |
| 12.00 to 12.24 | 10 hours | 5 hours | 2.5 hours |
| 10.00 to 11.99 | 14 hours | 7 hours | 3.5 hours |
| Below 10.00 | 18 hours | 9 hours | 4.5 hours |
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.