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SESK: Stuff Everyone Should Know · sesk.info/hame-battery-operating-time

How is battery operating time calculated?

Amp-hours divided by average current.

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  1. Average current divided by capacity in amp-hours
  2. Capacity in amp-hours divided by average current ✔
  3. Average current divided by internal resistance

Why: A 10 amp-hour battery feeding a steady 2 amps lasts about 5 hours. Capacity goes on top, current goes on the bottom.

Huh, didn't know that: A switching power supply is lighter because its high frequency inverter uses much smaller transformers and filter parts (E7D10).

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You know you might be a ham when your battery goes dead because you forgot to start the car before the long QSO.
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References

Answer: Capacity in amp-hours divided by average current. A 10 amp-hour battery feeding a steady 2 amps lasts about 5 hours. Capacity goes on top, current goes on the bottom.

  1. NCVEC 2024-2028 Amateur Extra Question Pool, E7D09 (4th errata, Feb. 4, 2026) www.ncvec.org/downloads/2024-2028%20Extra%20Class%20Question%20Pool%20and%20Syllabus%20Public%20Release%20with%204th%20Errata%20Feb%204%202026.pdf
    C. Capacity in amp-hours divided by average current
    Checked 2026-10-11.
  2. NCVEC 2024-2028 Amateur Extra Question Pool, E7D10 (4th errata, Feb. 4, 2026) www.ncvec.org/downloads/2024-2028%20Extra%20Class%20Question%20Pool%20and%20Syllabus%20Public%20Release%20with%204th%20Errata%20Feb%204%202026.pdf
    C. The high frequency inverter design uses much smaller transformers and filter components for an equivalent power output
    Checked 2026-10-11.

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