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Vent caps during lead-acid battery charging

Aviation Mechanic General (AMG) practice question 40 of 41 on Fundamentals of Electricity and Electronics. ACS element AM.I.A.R4 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONWhile a lead-acid storage battery is being charged, what should be done with its vent caps?

  1. ATighten them firmly to keep the electrolyte from spilling
  2. BRemove them completely and set them aside
  3. CLoosen them and leave them in place
Show the answer and explanation

Correct answer: C. Loosen them and leave them in place

  • A — incorrect Tightening the caps would trap the explosive hydrogen-oxygen mixture generated during charging.
  • B — incorrect The caps are loosened but left in place, not removed entirely.
  • C — correct A charging battery generates hydrogen and oxygen, so the handbook directs that the vent caps be loosened and left in place to let the gas escape.

BACKGROUND

When a storage battery is being charged, it generates hydrogen and oxygen, which form an explosive mixture, so steps must be taken to prevent ignition. The vent caps are loosened and left in place, and open flames, sparks, or other sources of ignition are kept away. Before disconnecting or connecting a battery to the charger, the power is always turned off by means of a remote switch. Electrolyte should also be handled carefully because sulfuric acid burns clothing and skin; if it contacts the skin, wash the area thoroughly with water and then apply bicarbonate of soda.

STUDY TIP

Three charging-area habits: caps loosened in place, no ignition sources, power off at a remote switch before touching connections.

KEY POINTS

  • Charging produces an explosive hydrogen-oxygen mixture.
  • Loosen vent caps and leave them in place.
  • Turn off charger power remotely before connecting or disconnecting.

SOURCES

  • FAA-H-8083-30B ch12 "Lead-Acid Battery Charging Methods" (charging safety paragraph)
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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.