Battery trigger and elapsed runtime estimate

Battery and work-cycle inputs

Method and worked example

Nominal Wh = V × Ah

Usable Wh = nominal Wh × usable %

Average W = tool W × duty; elapsed min = usable Wh ÷ average W × 60; trigger min = elapsed min × duty

Worked example: 18 V × 5 Ah = 90 Wh; 80% usable = 72 Wh. A 360 W trigger load at 40% duty gives 12 trigger minutes and 30 elapsed minutes.

Blank worksheet

Nominal V / rated Ah:

Usable percentage / usable Wh:

Tool W / trigger duty:

Trigger minutes / elapsed minutes:

Battery runtime result

Result recordPLANNING ESTIMATE

Worked example — default entered values

12.0 min trigger-on

30.0 min elapsed

72.0 Wh usable (144.0 W average)

Planning estimate with zero off-cycle draw; battery, tool and BMS behaviour govern.

Assumptions register

18 V × 5 Ah = 90.0 Wh nominal · 80% usable = 72.0 Wh · 360 W trigger load · 40% duty = 144.0 W average

Voltage and Ah refer to the same battery pack configuration.

The entered usable percentage may differ from the energy available in actual use.

Tool draw is constant when triggered and off-cycle draw is zero.

Temperature, age, discharge rate, startup demand, conversion losses and protection cut-off can change runtime.

△ Runtime can vary substantially

Tool behaviour, work rate, temperature, pack age, discharge rate, BMS cut-off and startup load can reduce runtime. Use only battery/tool combinations permitted by the manufacturer and stop for damage, swelling, leakage or unusual heat.

PLANNING ESTIMATE. Planning estimate only. Battery/tool interface, BMS limits, temperature, age, condition, startup load and manufacturer power/current limits govern.

Source register · registry version 1.0.0

Makita USA, Makita Expands 18V X2 (36V) LXT System with New Cordless Plunge Saw — effective 2017-07-31 — accessed 2026-07-24

Makita, 40V max ConnectX 1,500Wh Portable Power Supply — accessed 2026-07-24

Electrical Safety First, DIY-tool battery safety guidance: sanders — accessed 2026-07-24

Formula researched 2026-07-24