On subdermal battery protection

So, [insert typical lurker comment].

I am currently working on and testing a few ideas I have that require a small LiPo battery (https://www.adafruit.com/product/1317) , charging module, and qi charger, and I am wanting to discuss preventative measures and detection methods for subdermal batteries. At the moment, I intend on encasing the battery in a bio-inert metal box, which is open ended, and filling it with silicone and having the whole implant coated with silicone (though I haven't found a service for this, and am open to alternatives).

The main focus of my curiousity around the topic is about alternative casings/ways to secure the battery in case of a leak, and possible means of detection of possible leaks. Would a small pouch, which will decay when exposed to battery acid, filled with a dye and placed next to the battery do anything other than take up space; is it even feasible?

Please feel free to discuss possible failures/dangers of the battery and criticisms! Really any information or thoughts would be helpful at this point. I'm rather unversed when it comes to the implantation aspects, and really only have my imagination to guide me here, which isn't the most useful tool when you fail to imagine the limitations. (I am also still trying to read through the threads, so any links to this discussed in prior threads would be greatly appreciated!)

Comments

  • it sounds a bit stupid but step one of safe battery handling is to get a safe battery.
    Your average china-toy-powering lipo does not qualify as such. Skipping over the datasheet you are not supposed to charge it in ambient temperatures higher than 45°C (and the body temperature is not that far away). It also needs to be stored in a well ventilated room (suggests it may leak gas or hazardous liquids). It also has a very low cycle lifetime.

    While medical-grade batteries are hard to find I'd recommend to search for at least industrial quality batteries from reputable sources.

    I'd recommend to give Varta's CoinPower series a look. for example the CP 1654 A3
    Those sort of batteries come with extensive manuals covering each and every aspect of safe operation, safety mechanism, failure modes, charging instructions, circuit recommendations (even charging IC-suggestions) etc. Have a look at the handbook:
    https://www.varta-microbattery.com/wp-content/uploads/2018/02/HANDBOOK_CoinPower_en_FINAL.pdf

  • oh on a different note, you may want to use a battery technology that's not leaking or venting in first place (unless horribly abused). like NiMH can recombine the gas produced by overcharging within limits.

  • Every industrial battery I've worked with had a third of the power and cycle lifetime compared to a commercial one, go commercial or medical.

  • edited April 5
    Thanks! I'll definately look into medical batteries. Because my power needs are so low, I can be fairly indescriminant to the battery output, as well as the cycles. The project i'm focusing on just powers a single led attatched to a light guide film, with a reed switch to close the curcuit. Considering I would not be holding my magnet to the implant for 10hrs a day, maybe even in a week, I had estimated the battery's life cycle to last many years past the led burning out.
  • @crucible that's mainly because the industrial batteries are intended to be used for many years years while commercial batteries typically are allowed and desired to fail after 2 years. They hold up the same but the industrial datasheets are way more honest.

    @Torchwood , led's don't burn out, if properly operated they can do their job for decades. If you just want to light that thing once every few days for a couple of seconds you may be able to skip the rechargeable batteries and go with primary ones instead. There are types designed to last 10 years and more.

  • Leds can and will burn out given the right conditions, such as using at too high a voltage, and because I have altered my led to have a much thinner casing that can cause the leads to be more fragile, failure of the led is a small concern, though unlikely.

    I think I've decided to ditch rechargeble batteries and use silver oxide coin batteries (in series to get the desired voltage). I figure it will probably only last a year or two before the batteries die, and be pretty expensive (after coating and finding an implanter) for the length of time it'll be implanted, but will save a ton of space and make implantation easier without the bulky qi reciever and charging unit, and I will continue to look for alternative power sources that are less...risky, work on a small smart charger for it, and replace the original implant with the new one once the original fails. My ultimate goal use my original as a means to test the viability of a similar project that would have 2 or 3 leds and function as a flashlight. Hopefully in the coming years a solution will present itself.
  • be sure to pick a silver oxide battery that comes without mercury, just in case.

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