比德意志油布包怎样？

http://www.cia.gov/legacy/museum/artifact/rs-6-agent-radio-set/

This radio set and battery was hidden in Western Europe in 1961 and was not recovered until 1990. Had its use been necessary, the operator would have
activated the unit by adding water to electrolytic powder and poured the
solution into the battery.

这有什么稀奇的，混滋傻不知道以前车电池都可以加电解液？