28/10/2026
Ask Bill: What is reserve capacity?
Your battery’s reserve capacity tells you how long it can keep supplying power if your vehicle’s alternator stops charging.
Measured in minutes, reserve capacity is the time a fully charged battery can deliver 25 amps at 27°C before its voltage drops to 10.5 volts.
Why does this matter for your vehicle?
If your alternator fails, reserve capacity indicates how long the battery can continue powering essential electrical systems before its voltage drops too low.
What is a good reserve capacity?
It depends on your vehicle’s requirements. A reserve capacity of 90–120 minutes is common in many passenger vehicle batteries, but the correct specification varies by vehicle and battery type. A higher rating generally means the battery can sustain an electrical load for longer.
Reserve capacity is different from cold cranking amps (CCA). CCA measures a battery’s ability to deliver the high current needed to start an engine in cold conditions. Reserve capacity measures how long it can sustain a steady electrical load.
At Battery Corp, our branches are run by veterans of the battery industry with deep practical knowledge gained over years of experience.