December 2013
I want to encapsulate a circuit board with a small Li-ion battery in epoxy, for an outdoor, weatherproof project. Does anyone have experience encapsulating batteries? Is this a good idea?
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LiPo batteries which are probably what you are wishing to use do not like to be compressed, flexed, or prevented from expanding slightly during use. Encapsulating them in epoxy directly could do any and all to it, since the thermal expansion coefficient of the epoxy would differ than that of the battery.
There are other options, one of which is the inexpensive Lexan cases intended for protecting cellphones while camping sold at Walmart or other such stores. They have a silicone seal and clamping latch that protects the contents from moisture. If you needed to bring in signals or power, one could drill a hole, then feed the wire through and use RTV (silicone) to re-seal the hole. If you do this, route the wire from the bottom and drill a small drain hole that is at the lowest point. Air can pass through the cable itself, over time enough water vapor could collect in the case to become a problem under certain weather conditions.
Epoxy encapsulation is pretty drastic. Why not simply seal things in a plastic screw top container?! If the explosive nature of Li-ion cells is the concern, then you may be better off using the far more tolerant 3.2V rechargeable LiFePO4 (Lithium Iron Phosphate) version.
AA/AAA sized LiFePO4 cells sell for ~US$5 each, and are stated as good for 1000s of charge/discharge cycles too. See www.instructables.com/id/Single-AA-LiFePo4-cell-powered-project-in-a-parti/
