ESP32 board for UPS monitoring vs just using a Pi - am I overthinking this?

I went the Pi route for my basement setup about two years back and never looked at the micro option seriously, mostly because of the USB side. My UPS is a CyberPower and getting its numbers talking to anything that isn't a full Linux box was a chore. The Pi just ran the existing server software and it was done in an evening, no custom code to babysit when the vendor changes something in a firmware update. That said, the thing that actually killed my setup wasn't the Pi, it was the SD card. It corrupted after a hot summer in the garage and I lost the whole thing. Now it boots from a cheap external drive and has been rock solid since. On the remote access question, my honest answer is that I check it way less than I thought I would. The one time it earned its keep was when we were on vacation and the power flickered during a storm. Being able to see the battery was holding from a hotel wifi made the trip a lot less stressful. Whether that one moment justifies the setup is up to you, but it only takes happening once to feel worth it. If your ESP32 build already works and talks to Home Assistant, I'd just run it. Sunk cost works in your favor when the parts were sitting in a drawer anyway.

I built almost the same thing last spring for the closet shelf where my router and modem live, and I'd argue the micro route is the honest answer, not the detour. My board checks the battery every ten seconds and the whole thing sips under half a watt. The little computer I tried first idled closer to three watts, which felt silly for a job that's basially reading one number and repeating it forever. And with no memory card to corrupt, it just sits there doing its thing month after month. On the remote access question, I can answer from experiance. I set up the tunnel access because I figured I'd want alerts while traveling, and in six months I've actually looked at the page from outside the house maybe four times. But one of those was a long outage while we were staying at my in-laws, and knowing the battery still had plenty of charge instead of driving home to squint at a light was worth the setup hassle on its own. One thing I'd flag: put the board somewhere the WiFi actually reaches. Mine dropped off the network for a week before I noticed, which kind of defeats the whole point of the project.

I started looking into this setup too and was wondering about the power for the little computer. If the whole point is tracking the battery when the main power fails, does the ESP32 need its own seperate plug that is hardwired directly to the UPS? If the UPS is running off its backup battery, wouldn't the microcontroller also lose power and stop reporting data? I was worried about how the electricity gets to the board itself.

I'm still really new to this whole microcontroller stuff and I'm a bit stuck on the practical use cases. Since the UPS is running off its backup battery, even if the ESP32 is tiny, I keep wondering what the actual point of having all this data if it only gives me the current battery percentage. Do most people just use it as a real time status check, or are most people using it to trigger some automation? For example, if the battery drops below a certain level, shoud the system automatically send a text alert, or is just logging it to the history in Home Assistant enough?

I think the concern about the ESP32 losing power when the UPS runs on its backup is totally valid. If it's just plugged into the UPS, it might not survive the entire outage. I figured I needed something to handle the tricky power transition. I solved that issue by using a specific ultra low dropout regulator I picked up a while ago. That part held the line during the voltage dip when the UPS switched modes, which kept the microcontroller running untill the power came back.

Totally agree with the point about power draw; running a dedicated box just to read a status is overkill. It is definitely better to use the micro board for something like this. In my own setup for a workshop panel, I ran into some trouble with the signal dropping when the battery percentage was low. Turns out the metal filing cabinet right next to the ESP32 was causing massive interference. I ended up mounting the board on a small piece of plastic and pointing the antenna just enough to clear the ferrous material.