"something" = master relay contacts (generally bolted to the back or side of the
battery box), alternator slip rings, starter commutator/brushes, generator
commutator/brushes...

Jim



"G.R. Patterson III"
shared these priceless pearls of wisdom:

-gasses were produced as the alternator charged the battery and something set
it
-off.



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com