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Number of cells in a 24-volt lead-acid battery

Aviation Mechanic General (AMG) practice question 3 of 41 on Fundamentals of Electricity and Electronics. ACS element AM.I.A.K16 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONAn aircraft lead-acid battery is rated at 24 volts. How many cells are connected in series to make up the battery?

  1. A6 cells
  2. B12 cells
  3. C24 cells, one for each volt of rating
Show the answer and explanation

Correct answer: B. 12 cells

  • A — incorrect Six lead-acid cells make a 12-volt battery, not a 24-volt battery.
  • B — correct A lead-acid cell is normally rated at approximately 2 volts, so a 24-volt battery is composed of 12 cells in series.
  • C — incorrect Each lead-acid cell provides about 2 volts, not 1 volt, so 24 cells would give roughly 48 volts.

BACKGROUND

The voltage of a battery is determined by the number of cells connected in series. Although a lead-acid cell just removed from a charger reads approximately 2.2 volts, it is normally rated at approximately 2 volts. A battery rated at 12 volts therefore consists of 6 lead-acid cells, and a 24-volt battery is composed of 12 cells. Battery capacity is most commonly expressed as an ampere-hour rating, found by multiplying discharge current in amperes by the time in hours; for airplane batteries a 5-hour discharge period is the basis for rating capacity.

STUDY TIP

Divide the battery voltage by 2 volts per lead-acid cell to get the cell count.

KEY POINTS

  • A lead-acid cell is rated at approximately 2 volts.
  • A 12-volt battery has 6 cells; a 24-volt battery has 12 cells.
  • Capacity is rated in ampere-hours, on a 5-hour discharge basis for airplane batteries.

SOURCES

  • FAA-H-8083-30B ch12 "Battery Ratings"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.