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Both the descent and ascent stages of the Apollo Lunar Module were powered by silver-zinc batteries.

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Source: Apollo Lunar Module Electrical Power System Overview

The total weight of these batteries were 296 kg and 356 kg for the extended missions with longer stay on the Moon.

How much silver was at least left on the Moon by Apollo LM batteries?

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    $\begingroup$ Can I ask what's motivating this question? $\endgroup$
    – Russell Borogove
    May 12, 2020 at 21:11
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    $\begingroup$ ... and would it be enough to buy two tickets back to Earth?. $\endgroup$
    – user54
    May 12, 2020 at 21:28
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    $\begingroup$ Andy Griffith approves this question. $\endgroup$
    – DrSheldon
    May 13, 2020 at 4:54
  • $\begingroup$ @RussellBorogove This question shows how much effort was neccessary to provide enough electrical energy for the LM. $\endgroup$
    – Uwe
    May 13, 2020 at 14:19
  • $\begingroup$ @DrSheldon I never new about that! This weekend I'm going to procrastinate watching whatever I can find on Salvage 1 on YouTube instead of procrastinating by playing Stack Exchange :-) Related: Scholarly/journalistic speculation on Andy Griffith's career in drama if Mayberry hadn't existed? $\endgroup$
    – uhoh
    Dec 3, 2021 at 11:38

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TL;DR: 612kg

Well, as an approximate lower bound you can use the listed amp-hours of capacity and the battery chemistry to determine how many atoms of silver would be needed. To produce one amp-hour requires 3,600 Coulombs of charge. In silver-zinc batteries, each atom of silver is reduced twice, giving off two electrons.

A single electron has a charge of 1.602×10−19 Coulombs, so you would need (1/2) / 1.602×10−19 = 3.12x1018 silver atoms, or 3.12x1018 / 6.022x1023 = 5.18x10-6 moles of silver per Coulomb.

Multiplying this by the 3,600 Coulombs needed for one amp-hour, we get a minimum of 0.019 moles of silver per amp-hour. However, one cell of silver only produces ~1.55 volts, so the real battery has 20 cells. Therefore, we need 0.373 moles per full amp-hour. As silver weighs 107.87 g/mol, this would weigh 40.2g.

Finally, we can calculate the minimum silver for each type of battery:

LM Descent: 400 Ah x 4.5 batteries = 72.5kg of silver (out of 270kg total)
LM Ascent: 296 Ah x 2 batteries = 23.8kg of silver (out of 112kg total)
CSM: Returned to Earth.

Having 20-30% of the batteries be silver makes sense, as there was also roughly the same amount of zinc in the batteries, as well as electrolyte and a casing.

The descent stages obviously stayed on the Moon, and there were 6 of them: 72.5kg x 6 = 435kg.

The 6 ascent stages (which impacted the Moon after ascent): 23.8 x 6 = 143kg.

Also, although they were not included in your question, the lunar rovers used silver-zinc batteries of 23 cells each, and the batteries of the 3 lunar rovers, at 242 amp-hours each, would add 34kg of silver total.

Total: 612kg of silver, worth ~300,000 USD today. Of course, "Moon silver" would probably fetch a higher price.

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    $\begingroup$ Is your answer 2.5 tons? That's ridiculous. The whole LM weighed < 17 tons, wet. $\endgroup$
    – Organic Marble
    May 12, 2020 at 21:07
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    $\begingroup$ I assume IronEagle is talking about 6 LMs, not 1, but there's only 1647kg of battery, total, in the 6 descent modules on the lunar surface. en.wikipedia.org/wiki/Apollo_Lunar_Module#Descent_stage $\endgroup$
    – Russell Borogove
    May 12, 2020 at 21:11
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    $\begingroup$ I know, and that's still like .4 ton of silver per LM. No way. $\endgroup$
    – Organic Marble
    May 12, 2020 at 21:15
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    $\begingroup$ @OrganicMarble I think we found the final issue. $\endgroup$
    – IronEagle
    May 12, 2020 at 22:22
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    $\begingroup$ @IronEagle There's no need to call out the edits in your answer. Anyone who wants to look at the edit history can do so. It's confusing the way it's written now. Suggest editing to show only your current values. That way someone can read the question and see immediately what the answer is. $\endgroup$
    – Organic Marble
    May 12, 2020 at 22:22

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