[archi42]

This reads as if you did multiple API calls per "ping", and opened a new http connection for each API call?

Did you try reusing the http connection (one per ping)? How about putting all data in a single API call and let the server handle that?

Did you try compression? Not sure if compression makes sense, but a simple+fast compression like gzip could also be worth a try to reduce the actual bytes to put on the air; especially if your data is very verbose or repetitive. (Do that before connecting to wifi, even if that means not using http's compression).

I suppose you're talking http, not https. The latter will of course use much more energy.

Using UDP and the ensuring TCP-like qualities seems like a last resort solution.

Sorry if I misread your article and the suggestion were tried or are not feasible for you.