11 tools
Battery calculators
Batteries are described in units that are easy to mix up: amp-hours measure charge, watt-hours measure energy, and neither tells you how long something will actually run. These tools keep those apart and show the working.
Typical usable share of the pack
Same 100 Ah label, very different usable energy
LiFePO4 (lithium iron phosphate)
12.8 V nominal · No Peukert
Lithium-ion (NMC / NCA)
10.8 V nominal · No Peukert
AGM (sealed lead-acid)
12 V nominal · Peukert applies
Gel (sealed lead-acid)
12 V nominal · Peukert applies
Flooded lead-acid
12 V nominal · Peukert applies
These are typical published figures, not specifications, and every one of them is editable in the calculators. Depth of discharge is where most of the difference between chemistries comes from — before the Peukert effect is even counted.
Battery energy and capacity
Convert between the ratings printed on a battery and the energy figures used for sizing.
Ah to Wh Calculator
Amp-hours describe charge, not energy. Multiply by the pack's nominal voltage to get watt-hours, the figure you need for runtime, shipping limits and solar sizing.
Wh to Ah Calculator
Energy targets are quoted in watt-hours, but batteries are sold in amp-hours. Divide by your system voltage to find the capacity you actually need to buy.
Battery Usable Capacity Calculator
The label capacity is not the energy available to your load. Set the starting and minimum state of charge, battery health and conversion efficiency to expose the usable window.
Battery runtime
Work out how long a pack can carry a load once depth of discharge and conversion losses are taken into account.
Battery Runtime Calculator
Enter your battery and your load to estimate runtime. The calculator applies depth of discharge, battery health, conversion losses and — for lead-acid only — the Peukert effect, and shows each step of the energy budget.
Battery charging
Estimate charge time without pretending the finishing stage behaves like constant-current charging.
Battery Charging Time Calculator
Charging is fast while current is constant and slower near full. This estimate separates those stages, accounts for loads using charger current, and shows a range when lead-acid absorption time is genuinely variable.
Battery Charger Size Calculator
Choose a charging window and SOC target to estimate the DC amps a charger must supply. The model reserves time for current taper near full charge and adds any loads running while charging.
Battery bank sizing
Turn a daily energy budget and autonomy target into a chemistry-aware bank size and whole-battery layout.
Battery Bank Size Calculator
Turn daily energy use into the nominal kWh and amp-hours your bank needs. The model accounts for days without charging, conversion loss, battery health, usable depth of discharge and whole-battery rounding.
RV Battery Bank Calculator
Build an RV house-battery budget without applying inverter losses to native 12 V or 24 V loads. The result includes nominal kWh, Ah and a rounded whole-battery layout.
Battery configuration and rate
Plan series/parallel layouts and understand charge or discharge current relative to capacity.
Battery Series / Parallel Calculator
Series connections add voltage. Parallel connections add amp-hour capacity. Enter one battery's rating and the layout to see the complete bank without mixing those rules up.
Battery C-Rate Calculator
C-rate compares current with battery capacity. A 100 Ah battery at 20 A is running at 0.2 C; the same 20 A is 2 C for a 10 Ah battery.
Peukert's Law Calculator
Lead-acid batteries deliver less than their rated amp-hours when discharged faster than the test rate. Peukert's law estimates that reduction from the battery's rated current and exponent.
Methodology
How these tools are built
Every calculator here shows the formula it uses, the assumptions behind it and the limits of the model. Where a figure is a typical published value rather than a specification, it says so and lets you change it.