How this calculation works
Use the same identical-cell nominal voltage and capacity assumptions throughout. Series increases nominal voltage and parallel paths add nominal Ah; conversion efficiency and usable share each apply once to the energy budget.
Nominal Wh = series × cell V × parallel × cell Ah; runtime = nominal Wh × usable share × efficiency / load WA worked example
A 3-series, 2-parallel arithmetic model with 3.7 V and 2,500 mAh per cell gives 11.1 V, 5 Ah and 55.5 Wh nominal energy. At 80% usable share, 90% conversion efficiency and a constant 10 W load, modeled runtime is 3.996 hours.
Good to know
An ideal nominal energy budget, not a cell-discharge, charging or wiring design. No chemistry curve, aging, temperature, rate dependence, balancing, BMS cutoff or protection/rating selection. Nominal energy is not guaranteed usable energy.
Reference: Reference: model definitions and scope (opens in a new tab) ↗
Series voltage and parallel capacity enter different parts of the budget
For identical ideal cells, three at 3.7 V in each series path give a nominal 11.1 V. Two parallel paths of 2,500 mAh cells give 5,000 mAh, or 5 Ah. Multiplying nominal voltage and Ah gives 55.5 Wh, equal to six times the single-cell 9.25 Wh.
The cell counts describe an arithmetic energy model. They do not establish that particular cells, protection systems or connection methods are compatible. The reference discusses series/parallel behavior and real-cell limitations; the entered specifications remain your assumptions, not a recommended pack design.
The electrical power calculator describes a supplied DC point. Battery nominal energy combines voltage with charge capacity, with usable energy and load power stated separately.
Usable share and conversion efficiency apply once each
The default 80% usable share reduces 55.5 nominal Wh to 44.4 Wh. Applying an entered 90% battery-to-load efficiency leaves 39.96 Wh at the load. A constant 10 W load then gives 3.996 hours in the model.
Doubling that load to 20 W halves the simple energy-budget runtime. It does not model a chemistry’s rate-dependent capacity or changing conversion efficiency. A zero usable share gives zero modeled runtime even though the nominal energy remains nonzero; the tool does not silently add a second reserve or recover excluded energy.
A nominal-voltage current estimate is not a discharge curve
Battery-side current is estimated from load power divided by the entered efficiency and nominal pack voltage. Equal sharing between identical parallel paths gives a per-path estimate. Real voltage, current sharing, cutoff and usable capacity can change during discharge.
The electrical power calculator handles a separate DC voltage/current relationship. The LED series resistor calculator can model one explicitly supplied load case, but it does not supply a battery discharge curve. Temperature, aging, BMS behavior, quiescent draw and protection choices are outside this constant-nominal-voltage budget.
A few questions, answered
Are mAh and Wh the same measure?
No. Ah describes charge capacity; a nominal energy budget also needs voltage. One Ah is 1,000 mAh.
Does series connection multiply Ah in this model?
No. Identical series cells multiply nominal voltage. Identical parallel paths multiply nominal Ah.
Is the predicted runtime guaranteed?
No. It uses fixed nominal voltage, capacity, usable share, efficiency and load power, without a discharge curve.
Does this select a BMS or cell current rating?
No. The arithmetic does not assess cell compatibility, wiring, balancing or protection requirements.