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For those who like their questions to be 100% practical and serious, please look away now.

I've just watched "Raiders of the Lost Ark", which got me speculating about how to bring the booby-trapped temple into the 20th century. I reckon the first upgrade has to be to provide electricity, but how long can a battery sit on the shelf for and still work?

The longest shelf life battery I can find is a hertz horn these have been used to provide short bursts of power to detonate sea mines. Basically they have a glass phial of acid/electrolyte which when broken open, will cover a set of dis-similar metal plates and produce a small electrical charge. There are occasional stories of these mines being detonated decades after being laid.

Can anyone give me any idea of the likely lifespan of a hertz horn? Are there any batteries with a longer shelf life?

Update - I'm aware that any such battery is a one-time only thing, I was thinking that the battery would be initiated by the heroic explorer/villainous tomb-robber by mechanical means (i.e. treading on the glass phial), the electricity generated would be reserved for powering an entertaining death machine for said hero/villain. To actually detect an intruder electronically would require a power source to continuously work (i.e. remain powered and draw current) for hundreds of years - a different question all together.

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    \$\begingroup\$ Why go for something wimpy like batteries? Build your lair someplace where there's good access to geothermal energy. Get electricity from that, or use the heat directly to power your automatic doors and beheading machines. What could be cooler than mashing invaders flat with a burst of steam through a ram? Or just cooking them with a lengthy burst of live steam that they can't escape. \$\endgroup\$
    – JRE
    Oct 27, 2018 at 8:46
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    \$\begingroup\$ Related: electronics.stackexchange.com/a/402076/97482 \$\endgroup\$
    – jcaron
    Oct 27, 2018 at 8:58
  • \$\begingroup\$ The shelf life of a hertz horn is "as long as the glass isn't broken." Thereafter, you have a (small) lead acid battery that will run down and die. So, very much a one time deal. And, something has to mechanically break the glass for you to get power from the battery. \$\endgroup\$
    – JRE
    Oct 27, 2018 at 9:22
  • \$\begingroup\$ @JRE "one time deal" is a very useful construct, see henros' answer below... \$\endgroup\$
    – Solar Mike
    Oct 27, 2018 at 9:23
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    \$\begingroup\$ You might want to google "10,000 year clock". It's a clock that is designed to run unattended for 10 millenia. It captures energy from day/night temperature variations (significant in the Texas desert). Recall also the Jaeger-LeCoultre Atmos table clocks (commercially available, but fiddly and a bit on the expensive side). \$\endgroup\$
    – Spehro Pefhany
    Oct 27, 2018 at 9:26

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A battery using magnesium and silver plates, which is activated on contact with seawater, has an almost-infinite shelf life provided the plates are kept isolated from moisture and circulating air. Such batteries are used in emergency equipment (for example, submarine escape systems), where typically they are activated by removing sealing plugs and immersing the equipment. Naturally, they are extremely expensive.

When I worked for a manufacturer of rescue equipment, such batteries were produced as one-offs by a single specialist craftsman; each took nearly a week to construct. The design was proven by previous experience, as new batteries could not be tested without destroying them.

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