Smartwatch to make calls - best battery life

Android wear watches like Apple watches pretty much all have awful battery life apart from one brand, Mobvoi Ticwatch, due to dual screen tech Ticwatches tend to last 3-4 days.

However as you have said your not fussed about apps take a look at Honor, Huawei and Amazifit watches, these are smart'ish watches and although they have limited app support some will still allow phone calling over Bluetooth, fitness tracking etc....and some will give you 7+ days battery life.

Apple and WearOS Smartwatches pass calls from the watch to the phone, so the phone has to remain switched on (somewhere). You will also require a smartwatch specific phone tariff (with the same provider as the phone). That's how just having one number works.

TicWatch 3 & 5, Samsung Galaxy 5 Pro have best battery life. Most others, inc. Apple are ~ 1 day (charge overnight).

There appear to be Chinese 'no-name' smartwatches, which call direct, only requiring a standard SIM. Plenty on Amazon, etc. No idea how good they are. (edited)

I'd reconsider this. Thing is, smartwatches don't have the loudest speakers or the best mics, so they're not really great for making phonecalls with. They can be sort-of okay in some cases (like, I'd use mine if I was receiving a call while cycling down a quiet cycle path, at least until I could stop and use my phone properly), but generally, it's a thing I'd do out of necessity, not preference.

The best thing I've found for phonecalls is the Bose QC35 II. They're amazing, totally effortless to use, and offer really good call quality. It's as close as I've found to talking to someone as if they were in the room with you, and being a headset, your hands are completely free to do whatever while you're on the phone. I can easily do a 4hr+ call with them, while 90 mins is about my limit with a handheld phone, and about a minute is my limit with my smartwatch. They, or things like them, are really worth checking out, especially if you're wanting this so she can make calls without effort or that prohibit her from doing other things while she talks.

On the note of the Ticwatch btw, you've been recommended them a couple of times, but I'd strongly advise against them, and particularly against the Ticwatch 3. Problem is that Mobvoi just cannot be bothered to update the WearOS software on their watches, and because Google (among others) have withdrawn support for old versions of WearOS, Google Assistant and various other apps and features no longer work, making Ticwatches a bit deadweight. Mobvoi have been promising an update to 3.0 for over two years now, which seems unlikely to ever happen. Or, if it does, seems a little pointless, since they've dragged their feet on 3.0 for so long now that it also is outdated.