Safe battery for aquatic application

Hi - I am looking for appropriate battery chemistry to be used in a LoRa tracking device for wild turtles. The turtles spend some time in the water and can dive to a depth of about 10m. Although the tracker is in a waterproof enclosure, I want to avoid a catastrophe such as an explosion if there is a water leak. I purchased several Li-SOCl2 (Lithium Thionyl Chloride) 14500 batteries for use this spring but recently was told that Li-SOCl2 is not safe to use if there is any chance of water exposure. Is this a valid concern and if it is can someone suggest appropriate battery chemistry for my use case? The output voltage must be between 3.6 and 5.5 V and capacity ~2000 mAh. Lighter (preferably < 40g) is better and it doesn’t need to be rechargeable.

Thanks in advance,

Ned

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Direct reaction between water and internal cell components generally requires that the cell envelope be compromised in some way, and if the battery’s getting busted open it probably doesn’t bode well for the attached turtle…

It’s conceivable that moisture ingress could result in such a condition by causing a short circuit/excess discharge through some mechanism, but I’d imagine the more likely problem to be one of abbreviated battery life. Providing affirmative protection against water ingress through some means is probably a good idea; potting things in epoxy or silicone and using a reed switch or some similar non-contact turn-on mechanism would allow production of a nearly waterproof device with a decent storage life, albeit one that’s single-use. There are also softer, more readily removable materials available that might be useful if one wants to dig things out for replacement.

Any cell chemistry that offers a high energy density is, as a general rule, going to present greater hazards than one with a low density. A pair of standard alkaline AAs would certainly be a more benign choice on all fronts, but you’d need double the cell count. On the other hand, there’s not that much energy in cells of such size regardless of chemistry, so “explosion” is perhaps a bit of a strong word to use; it’s not as if one’s going to be seeing news reports of turtles sinking aircraft carriers here. Ignition on some level would seem a more likely edge case, which admittedly could still be a problem were it to occur in proximity to combustible materials.

Personally I do not know of any battery that is completely safe in an underwater application. For the size you are looking for, Lithium style will have the greatest capacity for the weight, It comes down to how well you water proof the battery housing

Thanks for your insight. My thinking at this point is to pot the tracker in silicone and put that inside sealed heat-shrink tubing. The heat-shink enclosure on its own proved to be watertight in my testing and with the silicone coating, it should be waterproof for the 6 weeks the trackers will be in the field.