Battery Capacity Runtime Chart

Use this worksheet after the calculator result to record voltage, amp-hours, usable watt-hours, load watts, depth of discharge, efficiency, runtime, series count, parallel strings, total battery units, and reserve notes.

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Quick reference table

A battery capacity runtime chart is a planning worksheet: 12 V x 100 Ah = 1,200 Wh, 80% DoD = 960 Wh, and a 400 W load = 2.4 h before reserve and module-count checks.

Battery runtime worksheet

Battery runtime worksheet
Item	Record from calculator	Follow-up
Battery	Voltage, Ah, series count, parallel strings, chemistry	Verify manufacturer limits
Usable energy	Wh after factors	Check DoD, temperature, and aging
Unit count	Battery unit voltage, unit Ah, total units, configured kWh	Review product architecture and parallel-string limit
Load	Watts and surge note	Separate critical and optional loads
Runtime	Hours or minutes	Compare with target autonomy

Battery runtime load-priority review

Battery runtime load-priority review
Runtime item	Record on worksheet	Why it affects backup planning
Critical load	Watts, priority, required hours	Runtime should be based on loads that must stay on
Surge load	Starting watts, duration, inverter response	Short surge can control equipment even when average watts are low
Depth of discharge	Allowed DoD, reserve, end-of-life factor	Nominal capacity is not fully usable energy
Battery block	Series units, parallel strings, configured kWh, margin	Rounded unit count can change capacity and architecture
Environment	Temperature, ventilation, enclosure, maintenance note	Battery performance and safety depend on installation conditions

Formula basis

Runtime hours = usable battery Wh / load watts. Battery units in series = ceil(bank voltage / unit voltage). Parallel strings = ceil(required Ah / unit Ah).

Usable battery Wh is nominal energy after depth-of-discharge, aging, temperature, and efficiency factors.
Load watts are the connected real-power load being backed up.
Battery voltage and amp-hours define nominal stored energy.
Battery unit voltage and Ah convert the bank screen into series count, parallel strings, and total unit count.
Reserve notes capture planned unused capacity and end-of-life allowance.

Worked examples

Backup load runtime recordRecord battery voltage, Ah, usable Wh, load watts, inverter efficiency, depth of discharge, runtime, reserve, and product follow-up.

48V LiFePO4 module-count recordRecord the required kWh and Ah, then screen 12.8V 100Ah modules as 4 series units by 8 parallel strings, 32 total modules, and configured kWh margin.

Medical refrigerator backup screenKeep running watts, compressor surge, required autonomy, battery voltage, usable Wh, depth of discharge, temperature note, and reserve in one runtime record.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

Battery runtime changes with discharge rate, temperature, age, chemistry, inverter efficiency, and manufacturer limits.
Battery unit count is an early sizing check only. Final series/parallel architecture depends on listed equipment, BMS rules, manufacturer instructions, overcurrent protection, conductors, ventilation, AHJ requirements, and review by a qualified installer.
The worksheet is a sizing record and does not replace product selection or safety review.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Use this chart as a battery runtime calculation record; verify battery manufacturer data, BMS and listed ESS architecture, inverter limits, adopted NEC energy-storage installation requirements where applicable, ventilation, protection, conductors, AHJ requirements, and review by a qualified installer before installation.

How to use this chart

1Record nominal capacityDocument voltage, Ah, battery count, series units, parallel strings, chemistry, and manufacturer basis.

2Apply usable factorsWrite DoD, efficiency, temperature, aging, and reserve assumptions.

3Compare with loadsUse usable Wh and load watts to check target runtime and backup scope.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Capture battery dataRecord voltage, Ah, series count, parallel strings, total units, nominal Wh, chemistry, and age factor.
Capture load dataWrite connected watts, surge notes, inverter efficiency, and critical load list.
Capture runtime dataDocument usable Wh, runtime, reserve, and product follow-up.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Using nominal battery capacity as fully usable capacity.
Treating a rounded battery count as a final listed ESS architecture.
Ignoring surge loads and inverter efficiency when estimating runtime.
Sizing runtime from average load without identifying critical-load priority, reserve, and end-of-life capacity.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Why is usable Wh lower than nominal Wh?

Depth of discharge, efficiency, temperature, aging, and reserve settings reduce the energy available for the load.

Can the worksheet choose the final series and parallel battery layout?

No. It rounds a planning count from voltage and Ah. Final battery architecture still needs product listings, manufacturer limits, BMS rules, protection, conductor, enclosure, ventilation, and AHJ review.

Can I size batteries from average watts only?

Average watts help, but surge loads, minimum runtime, discharge rate, and product limits still need review.