The reserve capacity of a battery measures how long it can deliver 25 amps before its voltage drops below 10.5 V. It gives a practical sense of the battery’s usable energy. Converting this figure into amp‑hours lets you compare it with other capacity ratings.
Multiply the reserve capacity by 60 to change minutes into seconds. For example, a 100‑minute reserve capacity becomes 6,000 s (100 × 60).
Multiply the time in seconds by the test current (25 A). This gives the total charge the battery can deliver: 150,000 C (6,000 × 25).
Since 1 A·h equals 3,600 C, divide the total coulombs by 3,600: 41.67 A·h (150,000 ÷ 3,600).
Reserve capacity ÷ 2.4 ≈ amp‑hours. This one‑step shortcut gives the same result.
