Arc already has a Low Power Mode - your phone’s Low Power Mode If you switch your phone into Low Power Mode then Arc will automatically adjust, reducing sampling frequency, deferring some non-vital processing tasks, and all of the scheduled background tasks. It will also switch to using an extremely minimalist UI instead of the normal full UI.
Though if you’re basing your assumption of Arc using the most energy on what you see in the Settings → Battery view on your phone, you’re likely being mislead. That view doesn’t mean what people think it means. (I’ve gone into long detailed explanations of why, elsewhere on the forum, if you’re up for a long boring read).
Arc is already extremely optimised, using as little energy as possible when recording. The only time it uses a lot of energy is when the app is in the foreground - building the UI, updating the map, etc. The rest of the time the app is using next to nothing.
So basically, the more time you play with the app in the foreground, the more battery it will use. But that is true of all apps - screen time is orders of magnitude more energy expensive than background time.
So you don’t need to treat Arc any differently from other apps in terms of energy/battery use. The more time you spend exploring apps, with the screen on, the more battery will be used. The more time the screen is off, the longer the battery will last. Whether it’s Arc or another app, it makes little difference.
For that you’re better off with something like Google Timeline. I don’t consider that the same class of app. That’s extremely low detail recording, which means most of the things Arc does become impossible - you can’t do much with that low level of detail and accuracy. It’s really outside the scope of what Arc is built for and built to do.
It also doesn’t save you much battery life either. Again, it’s not the recording that uses up battery, it’s the screen time. If Arc is using a lot of battery it’ll be because you’re using it in the foreground for a large amount of time.
Arc’s database is typically measured in gigabytes. It’s massive. Which means that sending the data over the network is extremely energy and network expensive - so much so that it can’t really be done on an iPhone.
Arc’s iCloud Drive backups get around this by the nature of how iCloud Drive works. When an app saves data to iCloud Drive it isn’t immediately synced - iOS decides whether to sync it to the server immediately or to delay the sync until later based on whether the phone is plugged in to power, connected to wifi, and a bunch of other measures.
Because Arc only does its backups when plugged in to power, it’s likely that the iCloud Drive sync will happen within minutes after. But importantly: that decision gets made by iOS, and the cost of that decision borne by iOS instead of Arc. Where as if Arc were to send its data directly to a server, it would bear the full cost of that energy expensive transfer, and be punished by iOS for it. Given the current constraints on iPhones, it wouldn’t end well.
There is however some small hope of eventually supporting other cloud storage providers! The Files app on iPhone (and the underlying systems) do support treating other cloud providers the same way as iCloud Drive, in that data can be saved onto them locally on the phone then later synced to the server when iOS decides it is appropriate.
The catch is that so far none of the other cloud providers have implemented the necessary parts of the “File Provider” interfaces on iOS. But once one of them does, I’ll be looking to enable that functionality in Arc!