KPC FIELD TOOL

BATTERY RUNTIME

How long will your battery last on an activation? Enter your battery and radio, pick a mode, and get an estimate before you leave the house.

🔋 Runtime calculator☀️ Solar charging⚡ LiFePO4 & SLA

Portable radio, lantern and battery box set up by the river at sunset

1 • Battery

CAPACITY UNITS VOLTS

BATTERY TYPE

2 • Radio

RECEIVE CURRENT (A) TRANSMIT CURRENT (A)

Use your radio manual’s numbers at the power you actually run. Transmit current is at full key-down power.

3 • How you operate

MODE TIME SPENT TRANSMITTING

OTHER GEAR ON THE SAME BATTERY (A)

Tuner, laptop, phone charging, lights… a phone charging is about 0.5–1 A at 12 V.

How it adds up

Field tips

Plan for about 70% of the estimate — cold weather, an older battery and a high SWR all shorten runtime.
Many radios shut down or distort as voltage sags. Lithium (LiFePO4) holds its voltage much better than lead-acid.
Dropping from 100 W to 50 W roughly halves transmit current. That's only half an S-unit (3 dB) at the other end. Power & S-units →
Charge a battery fully the night before, and bring a backup for long activations.

Estimates only. Average current is receive current while listening, plus transmit current while transmitting — reduced for SSB and CW because voice and keying don’t draw full power the whole time — plus any other gear. Check your battery’s and radio’s own specifications.