Ah and Wh
Wh = V × Ah; 1 kWh = 1,000 Wh
Compare Wh, not Ah alone, when battery voltages differ.
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Read the V and Ah on each old battery. Tell us how many are in series and parallel. If you know the equipment’s watts, add them for a tighter range.
The battery labels are enough to start. Without equipment power, the range will be wide.
If you have a capacity range, you can check it against the voltage, current and size of listed batteries.
Automatic matching covers deep-cycle use only. Starting, dual-purpose, regulated and other special uses need an engineering review. Also confirm charging, wiring, current sharing, dimensions, polarity and installation before choosing a battery.
Battery size depends on energy use, usable capacity and losses. Current limits and startup loads need a separate check.
Wh = V × Ah; 1 kWh = 1,000 Wh
Compare Wh, not Ah alone, when battery voltages differ.
Wh = Σ(W × hours × quantity × duty cycle)
A Wh input is already the total energy used during the selected period.
DC Wh ÷ DC efficiency + AC Wh ÷ inverter efficiency + standby Wh
DC devices and AC devices have different supply losses.
Required Wh = battery-side Wh × (1 + reserve) ÷ (DoD × temperature × health)
Less usable capacity means a larger battery is needed for the same load.
Runtime h = planned usable Wh ÷ average battery-side W
Temperature, ageing, duty cycle and conversion losses affect actual runtime.
A ≈ simultaneous battery-side W ÷ minimum working V
If the lowest operating voltage is unknown, the estimate uses 90% of nominal voltage.
Compare surge, inverter and BMS ratings at the same duration
A 5-second peak rating does not confirm that a longer surge is supported.
h = replace Wh ÷ (V × net charge A × efficiency) × completion factor
Nominal defaults: 95% charging efficiency and a 1.10 end-of-charge time factor.
Delivered Wh = nominal Wh × DoD × temperature × health × rate factor
Measured usable energy takes priority. There is no fixed Ah conversion ratio.
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