POTA Power Budget & Battery Runtime Calculator
Pick your radio, mode, and activation length — get the average current draw, the battery size that actually covers it (with a 20% margin), your runtime on the pack you already own, and the solar panel wattage that would sustain the draw indefinitely. Presets use manufacturer current-drain specifications, and the live-conditions hint tells you when today's bands support going QRP with a lighter pack.
Icom spec: TX max 3 A, RX 260–320 mA @ 13.8 V
~20% duty — voice peaks only
Running a pileup ≈ 50–60%. Hunting/casual ≈ 20–30%.
How the estimate works
The model is a deliberate approximation, and it is the same arithmetic experienced operators do on paper: your average current over an operating hour is the transmit current weighted by how much of the hour you actually transmit at full carrier, plus the receive current the rest of the time.
average A = (TX time × mode duty) × TX amps + (1 − TX time × mode duty) × RX amps
required Ah = average A × hours × 1.2 margin ÷ usable fraction of the chemistryMode duty cycles (approximations)
- SSB ~20% — voice peaks only, no heavy compression
- CW ~40% — key-down average
- FT8/FT4 100% — full carrier during TX slots (the slot cadence is what you set with the TX-time slider)
- FM 100% — continuous carrier
Chemistry usable capacity
- LiFePO4 — delivers approximately its full rated Ah
- Li-ion packs — ~90% usable
- SLA/AGM — plan on 50% depth of discharge, which is why a "12 Ah" SLA behaves like a 6 Ah LiFePO4 in the field
Radio presets are manufacturer current-drain specifications (Icom IC-705: TX max 3 A / RX 260–320 mA at 13.8 V; Yaesu FT-891: TX 23 A / RX 2.0 A per Yaesu's manual; Xiegu and Elecraft per their published specs). Spec values are maximums — your measured draw at reduced power will usually be lower, so treat results as conservative. The solar figure assumes ~70% of a panel's nameplate rating in good sun, the same rule of thumb used in our solar power for POTA guide.
Worked example: IC-705 on a 6 Ah LiFePO4
An IC-705 at 10 W running FT8 with a 50% TX cadence averages about 1.7 A — a 6 Ah LiFePO4 gives roughly 3.6 hours, and a 4-hour activation wants an 8 Ah pack once you add margin. Switch the same setup to SSB and the average drops to about 0.6 A — the same 6 Ah pack now runs ~10 hours. Mode is the biggest lever in your power budget, bigger than radio choice at the same power level.
| Setup (50% TX time, 4 h) | Avg draw | Needed (+20%) | Tier |
|---|---|---|---|
| IC-705, 10 W SSB | 0.59 A | 2.8 Ah | 3–4 Ah QRP pack |
| IC-705, 10 W FT8 | 1.66 A | 8.0 Ah | 6–8 Ah |
| FT-891, 100 W SSB | 4.10 A | 19.7 Ah | 20 Ah+ / power station |
Frequently asked questions
How big a battery do I need for a POTA activation?
For a 10 W QRP radio, a 3–6 Ah LiFePO4 covers a typical 2–4 hour activation on SSB; digital modes roughly triple the draw, so plan 6–8 Ah for FT8. At 100 W, a full-day activation wants 12–20 Ah. Run your exact setup through the calculator above — mode and TX time change the answer more than most operators expect.
Why does FT8 use so much more power than SSB?
FT8 transmits a continuous full-power carrier for the whole 12.6-second slot, while SSB only draws peak current on voice peaks (~20% duty). At the same dial power, FT8's average transmit draw is several times higher.
Do today's band conditions really change what battery to bring?
Yes — that is the point of the live hint. When 10m/15m/20m are open, 10 W works the same stations that need 100 W on a marginal day, and the difference is a 3 Ah pack versus a 15 Ah brick. Check current band conditions the morning of your activation.
Are the numbers exact?
No — they are conservative estimates built from manufacturer maximum-draw specs and labeled duty-cycle approximations. Real-world draw at reduced power is usually lower. For pack-buying decisions the 20% margin absorbs the error; for exact numbers, measure your own rig with an inline meter.