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There is a toy that is intended to be used in water. However, we found out that the battery box (holds 2 AAA's) is not water tight and water leaks into it. Is this an issue? I know that water is conductive.

So, essentially when water leaks in, the batteries are being shorted right?

How dangerous is this? Will it overheat the batteries? How dangerous is this for the user?

Is it going to shock my child to play with this toy in the bathtub?

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milesmeow
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    Please add more details about the toy and perhaps a photo? – hedgepig Feb 06 '13 at 20:49
  • For what it's worth, water is theoretically not conductive. Impurities in water make it conductive, so exactly how conductive the water is will change according to circumstances. Are you using the toy in salt water, like the ocean? – kojiro Feb 07 '13 at 12:46
  • @kojiro - yes the toy is something that can be used in salt water. – milesmeow Feb 09 '13 at 05:11

3 Answers3

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If I understand this right, you've got a electronic product that is intended to be used immersed in water, but it leaks and water can get onto the electronics. Seriously!!!?

In case you really are serious, yes, that is a problem. Even if the water only gets to the batteries, it can cause corrosion and will provide at least some leakage path for battery current, which will discharge the batteries prematurely. Pure water has pretty high resistivity, but it doesn't sound like you get to control the cleanliness of the water. Even a little salt, for example, will greatly increase conductivity.

There is little danger from the electric current since it will be largely inside the battery box, but again, seriously!? You are really thinking this might be OK somehow?

Olin Lathrop
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    Two words to add: environmental pollution. It is not just the electronics (and or user). – jippie Feb 06 '13 at 21:05
  • @OlinLapthrop - My gut feel was that this is going to short out the batteries and it will be an issue, but I just wanted to understand how severe of an issue this actually is. Thank you for your answer and confirmation. – milesmeow Feb 06 '13 at 21:12
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Apart from the fact the toy won't work for long, it makes it potentially very dangerous and absolutely not usable.

If *water gets to batteries, then they could be effectively shorted out (read low enough resistance to cause problems). There is a risk of rupture (or explosion/fire) which may cause the contents of the battery to leak into the water the toy is supposed to be used in. This also depends on the type of batteries used.

My view is that since it's a toy, however unlikely, you must assume that the worst case will happen.

*perfectly de-ionised water is not very conductive, however most water is well ionised.

For interest's sake, based on the comments below I took a glass of water and some salts, an AAA battery holder and hooked it up to my supply whilst immersed.
As expected, the "pure" water had very little conductivity at 3V, but with salts added a peak of ~0.3A was reached. Remember surface area is important with solutions, so it may be more with real batteries. With two copper surfaces of few cm wide/across 1A was reached easily. Not very scientific, but (hopefully) shows how the resistance can vary widely.

Anyway, here's a (bad, sorry) picture, note the bubbling from the negative electrode:

Experiment

Oli Glaser
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    I see no reason to believe that water would provide a sufficiently-low-resistance path as to cause a short-term leak of rupture. I would not be surprised if there would often be enough leakage to discharge batteries in less than a week, but I'd be surprised if there were enough to discharge them in less than a minute. My expectation would be that if the batteries will not be wet except at times when so much current is harvested that they'd be dead in minutes with or without leakage, the only effect of moisture would be to reduce battery life, provided batteries were removed when depleted. – supercat Feb 06 '13 at 21:55
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    `If *water gets to batteries, then they will effectively be shorted out.` Isn't that a bit too much? Sure, there will be a conductive path, but shorted out? That's overdoing it an by a lot. I just took my power supply, set it to 3.2 V (the upper limit of 2 AAA cells in my opinion), put the electrodes in pretty bad tap water with 5 mm distance and measured current. It never got more that 750 µA. – AndrejaKo Feb 06 '13 at 21:56
  • @supercat and Andreja - it depends - if used in a bath with bath salts, and the compartment is saturated, there will be low low resistance. If it's tap water, it won't be so bad. But who cares anyway? You have to assume worst case in this type of scenario. – Oli Glaser Feb 06 '13 at 21:58
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    @Oli Glaser You heard of the story about the boy who cried wolf? – AndrejaKo Feb 06 '13 at 21:59
  • @AndrejaKo - :-) I'll change it to "could be" then, is that okay? – Oli Glaser Feb 06 '13 at 22:15
  • @Oli Glaser That's OK with me. – AndrejaKo Feb 06 '13 at 22:27
  • The negative battery terminal in the photo has much greater surface area than would a battery or a sheet metal terminal. Most forms of metal aren't going to last very long in a saltwater environment even if there are no deliberately-induced electric current anywhere. A wind-up swimming toy, for example, may last reasonably well in fresh water and be rendered useless in a few hours in salt water. If the mechanics are only compatible with reasonably fresh water, the electrics might not make a huge difference. – supercat Jul 30 '15 at 15:35
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From experience with a weather station in the Scottish islands : it's not very dangerous because there isn't that much power from AAA batteries. Water won't short out batteries the same way a screwdriver would short out a car battery; the leakage would be milliamps rather than amps and heating is negligible.

Still, that will drain the batteries in hours or days. Worse (especially with salt water!) the battery powers spectacular electrolytic corrosion, dissolving copper wires, the battery casing, component leads and PCB tracks anywhere the water can reach, quickly rendering the thing useless and ... quite difficult to repair.

  • In addition, even pure, deionized water that is not initially conductive will not stay that way for long as it will quickly pick up contaminants from the environment. This includes minute amounts of residue left on PCBs from manufacturing. Once electrolytic corrosion starts, a lot of ions will be picked up and corrosion will accelerate as the conductivity of the water increases, usually until the battery is discharged or enough of the wiring is destroyed to break the circuit. – ajb May 07 '20 at 23:21