We recently released (pun intended) our drop-off design to open source, which you can read about here: https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.1...
However, this is a timer version. You can potentially use a pretty small lithium polymer battery, provided it has a pretty decent discharge (or 'C') rating. Something like this would be ok I reckon: https://tinyurl.com/yxhxkolm and we usually use this one: https://tinyurl.com/y3hv6oh6 . . . You might have to do some experimenting with the gauge of nichrome used as the heating element. I've found with some recent tests, that 32AWG gauge nichrome (e.g. https://tinyurl.com/yxtx9wao) in a coil of about six-ten turns around something like a full size paper clip can reliably melt nylon line with <1A of current from a 3V primary cell (e.g. CR123). I can post some pictures if none of that is clear.
In therory, you could adapt the system to greater strength requirements as needed, although as the nylon line gets thicker, you might need more powerful batteries and bigger gauge nichrome to make sure it all separates properly. I've only tested up to 45kg/100pound line. I dunno about elephants though as I think they are rather a big animal, is that correct @pwrege ? :) :) I am certainly happy to try and help develop a bigger, stronger system, as I have a lot of nichrome and bits of pieces here I can mess around with so let me know...
And a remote version is certainly possible, but we haven't gone down that development line. Some sort of duty-cycled (only on every now and then) receiver would be the way to go I'd imagine. But a small VHF transmitter on the dropped device could also help find a timer version, as the receiver version might take a bit to develop.
I actually made a prototype version recently for birds that has no electronics apart from a battery, the nichrome release wire and nylon line and a magnetic reed switch, such that if a magnet gets near the device it detaches. It'd only work obviously if either you know you can get close to animals (these were for urban magpies that happily come close), or they habitually return somewhere like a nestbox.
@wildtrack those injuries are absolutely horrendous. I've actually, briefly messed around with turning our drop-off into a two-stage system that expands as an animal grows, and then drops off later. I haven't gone too far with it, but I'd be really interested in getting it right to avoid things like what you showed. Just awful.
@KylerA I am super glad you got a system that worked for your Crittercams! Telonics do make awesome gear.
More than happy to discuss further.