Battery choice for wildlife VHF transmitter refurb

Thread Starter

kjloope

Joined Mar 1, 2022
3
Hi All,
This is my first post at AAC; it looks like a great place to come for advice about battery selection for my project. I'm trying to refurbish some wildlife radio transmitters. The manufacturer wants $165 to refurbish each one, when all they need is a new battery. I've not been able to determine the original battery type, as they are completely unmarked; see attached photo. The originals are of unknown age and the xmitter that still has a charge and functions has a measured voltage of ~3.4V. The batteries are basically hooked up in parallel, with each positive terminal wired separately to the chip. Hooking one of these positive terminals to a spare 3.7V 1200mA flat-style lipo battery from adafruit seems to work perfectly.

My questions are:
1. Does anyone recognize this battery type? I'd prefer to replace with the original type if it can be found. Dimensions of each are ~1 1/8inch long by 1/2 inch diameter. The terminals are solderable. They are completely unmarked.

2. If i can't replace with the original battery type, my next best option would be to select an alternative 3.7V battery. Keeping the profile and weight roughly equivalent to the original is important, as these will be encased in hard epoxy and attached to tortoises. The transmitters are very low drain, and can last for 1-2 years on the original batteries. The flat lipo batteries are attractive given how flat they are. If encased in hard epoxy and then attached with putty epoxy, do these seem like a good option for deployment for 1-2 years at a time? The (encased) batteries will be exposed to the Florida summer sun when the animals bask, and experience long periods at ~40 degrees F in the winter. Are there there reliability or safety concerns that could be mitigated by selecting an alternative type of battery? I've found somewhat conflicting information online about lipo vs lithium ion vs other types of lithium batteries.

Many thanks for any and all thoughts on this!
 

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Ya’akov

Joined Jan 27, 2019
5,659
Sorry for being so fragmented but here is what I know without more information.

The specs for the battery that will be most critical for you are:

  • Self-discharge rate (this will limit lifetime even without transmitting)
  • Ambient temperature tolearance (particularly to cold)
  • Maximum open circuit voltage (importance depends on the tranmistter)

Lithium cells have some attractions but I would not consider secondary cells. You don’t need recharging and it brings disadvantages especially for pouch cells like LiPos. Given the size and power requirements, a tabbed CR123A lithium primary battery might be very good, but, cold temperatures definitely reduce the capacity of lithium cells, sometimes substantially.

10 Panasonic CR123A Lithium 3V Batteries w/ Solder Tabs - NEW - Exp 6/2031

I might be able to help more with more information. There are other more exotic options but that may not be necessary. Given the need for reliability I would certainly recommend testing in whatever temperatuse extremes can be expected.
 

Thread Starter

kjloope

Joined Mar 1, 2022
3
Hi Yaakov,
Thanks for all of your thoughts. I don't know if the original cells are primary or secondary, but I assume they are primary (non-rechargeable).

The manufacturer of the xmitter is Holohil, but the cells themselves have no labeling. Understandably, Holohil doesn't want to provide any info, as they are in the business of selling new ones and refurbishing old ones.

The dimensions of the LiPo pouch cells are really appealing, as it is nice to have a low profile on the back of the animal so it does not catch on vegetation and the burrow entrance. Could you elaborate on why they would be unattractive for this application? An alternative we have used for other types of transmitters deployed in the same environment is the CR2477, which I believe have similar chemistry to the CR123A. These held up fine in our environment, so that's a good sign for the CR123A, i would think, though i guess different manufacturers could have different tolerances, etc. However, I hooked up a CR2477 to the xmitter and it did not function properly. Could be that it's a dud cell (i'll try another this afternoon), or that the device requires the higher voltage of the 3.7V batteries and can't handle the 3V (unless i'm misunderstanding something).
 

Ya’akov

Joined Jan 27, 2019
5,659
The lithium pouch cells will have a higher self-discharge rate (up to 5%/month), they are more fragile, and they are more temperature sensitive.

The CR123As are also not the best performer for self-discharge and temperature sensitivity but compared to the pouch cells they are better.

The best option would be LiSOCI₂ cells. They are used in industrial applications. Particulary the cells with bobbin-wound construction which have as low as 1%/month self-discharge and an really wide operating temperature range.

Here’s a candidate for your application. It would be a really good choice is it is physically small enough and it’s relatively high open circuit voltage of 3.8V is not a problem, though I don’t think it would be, it could be. By the way, the LiPos could have that same problem.

1646234358970.jpeg
 
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