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BATTERY PLANNING, MADE CLEAR
Battery Calculator for your backup.
Explore nominal capacity, compatible series/parallel counts and indicative backup time with clear battery assumptions.
Plan your battery capacity.
Watts the battery-backed equipment will use. Starting surges need a separate check.
How long you want the running load to operate. This is a planning target.
Use the DC bank voltage specified by the inverter or UPS, not the AC output voltage.
Each string has the series batteries needed for the bank voltage. Use whole numbers.
Bank & efficiency assumptions
Replace the example battery voltage and Ah rating with your compatible battery data. Series/parallel wiring must be permitted by the manufacturer.
Example: 12 V for a 12 V block. Use the battery data sheet; lithium blocks may use 12.8 V.
Use the Ah rating and its stated discharge rate. Actual usable capacity varies with load and condition.
Share of battery energy reaching the AC load. Replace the starting value with equipment data.
Share of nominal energy allowed for discharge. Follow the battery and system design limits.
Remaining capacity after age, temperature and discharge-rate allowances. This is not a discharge curve.
Estimates stay in this tab. Contact details are shared only when you request a report.
Your calculation, explained.
The first submission is checked on our server. Further edits update this private on-screen preview instantly.
Live preview updated from your current values. The original enquiry remains saved; these edits stay in this tab unless you email an updated PDF.
Inputs & assumptions
Calculated results
Battery runtime vs running load
How the numbers are calculated
BEHIND YOUR ESTIMATE
Energy, capacity and compatibility.
Wh measures stored energy; Ah measures capacity at a specified voltage. This tool estimates a compatible arithmetic bank layout and backup time using the assumptions you enter. It does not approve a battery or wiring arrangement.
What is the difference between sizing and checking a bank?
Sizing starts with load, target time and bank voltage to estimate minimum nominal Ah, then rounds up using your entered battery blocks. Checking uses your bank voltage, block voltage, Ah and parallel strings to estimate the bank’s energy and indicative runtime.
How do series and parallel affect the result?
Series connection adds voltage while Ah stays the same. Parallel strings add Ah at the same bank voltage. Bank energy is voltage multiplied by bank Ah. The bank voltage must be a whole multiple of one block’s nominal voltage, and the manufacturer must permit the arrangement.
Is the backup time guaranteed?
No. Rated Ah depends on discharge rate, chemistry, age and temperature. The energy allowances are simplified; actual battery curves, BMS, cutoff voltage and inverter performance must confirm runtime.
What can I carry to the UPS calculator?
Use the transfer link to carry running watts and target backup minutes. Checking mode can carry its indicative estimated minutes. UPS growth and battery assumptions do not transfer. The UPS tool supports transferred times up to 480 minutes; longer times need individual review.
Reference: Victron Energy — series, parallel and energy. Verify the final design with appropriate site and manufacturer data.