Understanding Car Battery Reserve Capacity and Electrical Formulas
Reserve Capacity (RC) is a vital metric used in automotive electrical engineering to evaluate how long a vehicle battery can sustain essential electrical loads if the alternator fails. Unlike Amp-hours (Ah) which usually measure a 20-hour discharge rate, Reserve Capacity measures the time in minutes that a fully charged battery at 80°F can continuously supply a constant 25-ampere load while maintaining a terminal voltage above 10.5 volts for a 12V system.
The Formula Used
To calculate realistic performance under variable loads, this tool applies Peukert’s Law along with environmental adjustments. Peukert's Law addresses the fact that a battery's available capacity decreases when the discharge rate increases:
$T = H \times \left(\frac{C}{I \times H^k}\right)^k$
Where T is discharge time, C is rated capacity, I is discharge current, H is time base rating, and k represents the Peukert coefficient.
How to Use This Calculator
Input your automotive battery parameters across the three configuration columns. Specify your rated Amp-hours, target discharge current, operational temperature, and health factors. Click the calculation button to immediately review time performance, minute yields, and total energy capacity above the form.