Portable Horn Battery Runtime Calculator — Cordless Pack Life
How long does a cordless 18V battery pack last on a portable train horn? Anchored to 25 A @ 18 V (~450 W) load with Peukert and condition derate.
Battery platform
Pack capacity
Pick a common pack size or set a custom capacity.
Pack condition
Honking pattern
Wall-clock runtime
48.5 min
At 20% duty cycle (1s on, 4s off) the same pack keeps you honking for 48.5 min of total session time — about 582 individual blasts before the compressor stalls on a flat pack.
Power draw
- Compressor power
- 450 W
- Current at pack
- 25 A @ 18V
- Pack C-rate
- 5 C
Usable energy
- Label capacity
- 5 Ah · 90 Wh
- After Peukert + condition
- 4.04 Ah
- Energy delivered
- 71 Wh
How the math works
A portable handheld horn compressor pulls a measured 25 A at 18 V under load — about 450 W at the motor. On a higher-voltage pack the same wattage is split across more cells, so the per-cell C-rate drops and Peukert losses shrink.
I_pack = 450 W / V_nominal Ah_peukert = Ah × (Ah / I_pack)^(k − 1) k = 1.08 Ah_usable = Ah_peukert × condition_factor t_continuous = Ah_usable / I_pack t_wallclock = t_continuous / duty_cycle n_blasts = t_continuous / blast_seconds
Power-tool li-ion packs have a flatter Peukert curve than lead-acid (k ≈ 1.08 vs 1.2 for AGM), so a 5 Ah pack at 25 A gives close to its rated capacity — but cold cells, cycle wear, and BMS low-voltage cutoff still take a real bite. Treat the result as ±15%.
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