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I am trying to make equipment to measure temperature in small mammals, probably attached to a neck collar. The collar needs to be very lightweight (e.g. <3g total) so I am planning to use a lithium coin cell battery, perhaps the 16mm ones or posssibly 12mm. I was thinking of buying one with contacts attached and just glueing it to the board to save weight.

Apart from the connection to the board I don't want to run the risk of the contacts on the battery touching anything else, and it would be better if it is somehow covered to make it much more difficult for the animal to scratch or bite (I would try to make it so that the entire collar comes off if the animal uses enough force rather than just the battery). I'm also not sure about the requirements for waterproofing. The animal will probably get wet and might drag the collar in a river when drinking.

Can I cover the battery (and probably rest of the circuit apart from the sensor) with some type of sealant or do these batteries need vent holes to be safe? Any suggestions on lightweight ways to enclose and protect anything from the enviroment, (ideally which could somehow be removed later to replace the battery, even if requiring tools) would also be appreciated. perhaps I could use some type of material or something and heatshrink inside that, but I'm concerned about water also. Thanks!!! :)

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    \$\begingroup\$ Wondering who has the courage to suggest something that is dog chew proof after you added all those concerns.... I'm going to pass. \$\endgroup\$ – Trevor_G Dec 22 '17 at 2:16
  • \$\begingroup\$ it's ok, I'm an overly cautious person, they are bats rather than dogs and quite small, and whatever people suggest if it doesn't seem to be enough I will change it :p and test on captive bats beforehand. But I'm not sure if it's safe to completely cover a battery or how to make them water safe... \$\endgroup\$ – S.H. Dec 22 '17 at 2:41
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    \$\begingroup\$ you could make a test device out of just a battery and an LED (like a keychain light) , maybe a series resistor ... and pot the whole thing in epoxy, just to see what happens. \$\endgroup\$ – jsotola Dec 22 '17 at 4:35
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    \$\begingroup\$ Rest easy, in the past just for kicks I have dead shorted these type cells, because I had a load of leaded ones, that were given to me. They were new and and at full voltage. The internal resistance, and the lack of power stored, prevents them from doing anything remotely bat unfriendly. T \$\endgroup\$ – Sara Heart May 25 '18 at 2:33
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    \$\begingroup\$ Potting them would prevent the poor mosquito eaters from getting any leakage on them. I just did this again, (new lithium cell type BR2325t2) with my Fluke meter on a ten amp scale, and current dropped too fast to even get a usable initial reading, then went to a few mA without even warming up. I like destructive testing, but this test was boring. \$\endgroup\$ – Sara Heart May 25 '18 at 2:50
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We often use a hot glue gun on these applications. It will take care of most of your concerns.

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    \$\begingroup\$ I question the long term environmental resilience of hot glue. \$\endgroup\$ – Nick Alexeev Dec 24 '17 at 23:47
  • \$\begingroup\$ hmm, thanks!! Do you think I can I cover the entire battery with hot glue without causing problems? (after first soldering the contacts to the rest of the board of course), i.e. for waterproofing. \$\endgroup\$ – S.H. Dec 25 '17 at 8:29

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