Battery shopping starts with capacity in amp-hours—but energy planning needs watt-hours. This guide walks through the battery capacity Ah to Wh calculator: rated Ah, bus voltage, and stored Wh for fair pack and bank comparisons.
Benefits
- Rated Wh = capacity Ah × nominal system voltage.
- Compare 12 V, 24 V, and parallel/series banks on one energy scale.
- Input for runtime, $/Wh cost, and inverter autonomy estimates.
How it works
- Enter nameplate amp-hour capacity (per bank or single pack).
- Add nominal bus voltage your loads connect to.
- Read total watt-hours—use for cross-listing and bank sizing checks.
FAQ
How do I convert battery capacity from Ah to Wh?
Wh = Ah × V. Example: two 100 Ah 12 V batteries in parallel → 200 Ah × 12 V = 2,400 Wh bank. In series (same 100 Ah cells): 100 Ah × 24 V = still 2,400 Wh—Ah and V trade off but Wh stays the product.
Does chemistry change the Ah to Wh formula?
No—Wh = Ah × V regardless of LiFePO4, AGM, or lithium-ion. Chemistry affects usable depth-of-discharge and cycle life, not the conversion. Apply DoD after rated Wh: 1,200 Wh rated × 80% DoD ≈ 960 Wh usable.
Why do retailers list Ah instead of Wh?
Deep-cycle and starter batteries historically marketed amp-hours at a standard voltage—often 12 V or 20 hr rate. Wh makes cross-voltage shopping honest. Run every quote through Ah × V before comparing a 300 Ah 12 V deal to a 150 Ah 24 V rack.
Technical specifications
- Bank Wh = total_Ah × bus_V.
- Parallel: Ah add, V unchanged. Series: V add, Ah unchanged.
- Usable Wh = rated Wh × DoD fraction.
- Related: battery-bank-size, battery-cost, wh-to-ah.
Nameplate Ah is only half the capacity story
A 400 Ah sticker at 12 V is 4,800 Wh. A 200 Ah sticker at 24 V is also 4,800 Wh—same energy, different wiring. Battery capacity Ah to Wh math exposes that parity before you buy four heavy 12 V boxes when two 24 V units would store identical energy with less parallel cabling.
Banks in series and parallel
Parallel strings add amp-hours at constant voltage; series strings add voltage at constant amp-hours. Wh is conserved in both layouts when cell count and chemistry match. Enter the bank totals—not single cell specs—into the calculator. A 4×100 Ah 12 V parallel bank is 400 Ah × 12 V = 4,800 Wh; verify your BMS and inverter voltage match that bus.
From rated Wh to what you can actually use
Rated Wh from Ah × V is the full tank; usable Wh depends on chemistry and BMS cutoff. LiFePO4 may safely deliver 80–90% of rated Wh; lead-acid often 50%. Multiply rated Wh by your planned DoD before runtime math. This calculator gives rated energy—the next step is Battery Bank Size or Runtime with your real discharge floor.