Would a button cell battery contain mercury? If so, why?

I was wondering if an alkaline button-cell battery that says $0~\%\ \ce{Hg}$ is actually completely mercury free or if it is still considered to have traces of mercury. Why do some batteries say no intentionally added mercury? Where would the unintentional mercury come from? Just wondering because I accidentally washed my son's little toy watch in the washing machine and it contained one of these types of batteries. Is it okay to use my washer or could it be contaminated?

Also, I use disinfecting wipes around the house quite a bit that contain dimethyl. Could using these wipes around where the battery was create dimethylmercury?

• First take some slow breaths and calm down. EVERTHING contains at least trace amounts of all the elements. Your washer is fine, and using wipes won't create dimethyl mercury. – MaxW Oct 18 '17 at 4:23
• Button cells can be dangerous for more reasons than that they contain poisonous components. They are a big danger to children if swallowed, though mainly because they set up corrosive currents through tissue. Even mercury containing ones, though, pose no hazard if they are undamaged as they are usually well sealed against leaks. – matt_black Oct 18 '17 at 22:29
• Anybody care tell me what exactly is dimethyl? – Karl Oct 18 '17 at 23:22
• @Karl - Dimethyl benzyl ammonium chloride is evidently a common wipe component, but the dimethyl could be from something else. The OP is obviously clueless about chemicals. – MaxW Oct 19 '17 at 1:46

Mecury batteries were indeed once popular. In the charged state, they contained mercury(II) oxide $\ce{HgO}$ and zinc metal as the active components. During use, the overall reaction would be:

$$\ce{\underset{\text{mercury(II) oxide}}{HgO} + \underset{\text{zinc}}{Zn} -> \underset{\text{mercury}}{Hg} + \underset{\text{zinc oxide}}{ZnO}}\tag{1}$$

As you can see from the equation, these batteries would produce mercury while decharging so in the fully decharged state practically all mercury(II) oxide would be converted to elemental mercury. Mercury(II) oxide is toxic on indigestion while elemental mercury is toxic especially when inhaling vapour. The latter can also accumulate in the environment meaning disposing these batteries was a significant issue. This is why the US and the EU banned the advertisement and sale of batteries containing a certain percentage of mercury in the 1990’s as the Wikipedia article explains.

The battery in your son’s toy watch obviously was not a mercury battery since it reads $0~\%\ \ce{Hg}$. Nowadays, various different types of batteries are used in button cells, replacing the formerly popular mercury cell type; usually lithium or alkaline cells. These do still come with their own specific dangers — most notably, batteries should always be disposed of properly and never with household waste for environmental reasons — but do not contain compounds as toxic as the mercury compounds in mercury cells.

Therefore, your washing mashine is not contaminated with mercury and still safe to use.

On to your side questions. I don’t exactly know what the active compound in your ‘dimethyl wipes’ is, but I can assure you that it will not react with mercury to give dimethyl mercury. Chemistry is more complex than just taking word roots and putting them together. A common German chemists’ joke actually plays on the word root thing, causing laughter with those who know how absurd it is thanks to the similarities of the German words for strawberry (Erdbeere), blackberry (Brombeere), the ground or earth (Erde) and bromine (Brom). It suggests throwing a blackberry on the ground so that it reacts with earth to form a strawberry and liberate bromine.

Finally, your unsureness about the ‘intentionally added’. If your analytical instrument is good enough, you can practically detect every element in every sample. This is especially true for samples of similar types; i.e. metals will always contain other metals as trace impurities. However, these contaminants are present in absolutely minute traces. We are talking one part per billion or even less. Among these impurities there is indeed likely mercury. But these concentrations are so low that they do not matter for any practical purposes. I assume that the manufacturer of the battery simply didn’t want any super smart jackarses coming who throw the full blow at one of those to determine $\pu{0.1ppb}$ mercury and proceed to sue the company in the US.

• Fünf Mark in die Schlechte-Wortspiel-Kasse für den Schenkelklopfer mit der Brombeere. – Karl Oct 18 '17 at 23:22