Power Bank Charge Count Calculator – Estimate Recharges

Budget mixed-device charging sessions using the bank inputs on this page.

Count one device’s sessions or budget a mixed-device plan

The original calculator estimates how many times the bank can supply one device over an entered charge range. The additional budget combines different battery sizes, ranges and session counts. Both use watt-hours; dividing two mAh labels directly is valid only when the voltages and energy basis match.

Use energy ratings on a consistent basis

Nominal battery Wh = mAh × its paired nominal voltage ÷ 1,000. Use the manufacturer’s Wh rating directly when available. A bank’s internal-cell voltage is not automatically its USB output voltage. In the original calculator, the device’s voltage belongs to its own battery rating. A percentage gauge is treated as a proportional energy fraction, which is an approximation.

The manufacturer’s power-bank label explanation distinguishes stored capacity, input specifications and output specifications. Check the exact label and manual rather than inferring an energy rating from the largest port wattage.

Understand the single-device result

Delivered battery energy = bank Wh × available charge % ÷ 100 × overall delivery efficiency % ÷ 100. One selected session requires device Wh × (target % − starting %) ÷ 100. Dividing delivered energy by session energy gives an estimated session count. The whole-session result rounds down; a remainder is a fraction of another identical selected session, not automatically a complete recharge.

A 20%–80% session replaces 60% of the device’s nominal energy. Full-energy equivalents instead divide by the complete device Wh. These answer different questions. The original single-device target must exceed its starting percentage.

Allocate energy to several devices

In the mixed-device budget, reserve means percentage points of the bank’s rated charge retained at the end. With available charge A, reserve R and efficiency E, usable delivered Wh = bank Wh × (A − R) × E ÷ 10,000. The reserve cannot exceed the available charge. It is not another efficiency deduction.

For each row, required Wh = device battery Wh × (target − start) ÷ 100 × planned session count. Sum all rows and compare that demand with the delivered budget. For example, a 37 Wh bank at 100% available, zero reserve and 85% efficiency supplies 31.45 Wh. Two 20%–80% sessions for a 19.25 Wh phone require 23.1 Wh. One full 7.2 Wh camera session adds 7.2 Wh, leaving 1.15 Wh after the combined 30.3 Wh plan.

“Complete repetitions” repeats the entire list and all its session counts together. It does not select the most important device. The minimum-rated-Wh result keeps the entered availability, reserve and efficiency fixed. No finite bank size can supply a positive plan when availability equals reserve. A zero-session or unchanged-charge row requests zero modeled energy.

Limits and the next decision

Use 1–20 device rows, positive device Wh up to 100,000, charge percentages from 0–100 and whole session counts from 0–1,000,000. The budget accepts plain decimals up to 18 places and compares exact rational energy before display rounding to six places. Editing source or plan inputs clears the old budget result. The illustrative rows are not device specifications.

Energy coverage does not establish port count, USB negotiation, simultaneous power capability or charging time. Active device use, battery wear, temperature and gauge error can change the requirement. Include extra energy explicitly rather than assuming the displayed headroom covers it. Use Power Bank Runtime for watts over time, or Power Bank Charging Time to refill the bank itself. Calculations do not save device records.