Yes actually they do. As mustang mentioned the phone will learn your usage patterns adjust some settings accordingly. Additionally, while you said your first day was typical use, setting up the phone takes a toll on the battery life. Setting up your accounts & syncing your data, downloading apps to you had on your previous device, customizing your settings, & first connection to the network all drain the battery. I've found it isn't a bad idea after you're done setting up your phone, shut it off or restart it, charge it, then go from there.
I have the 4a & the first few days I wasn't all that impressed with the battery life. But by the end of the week, it changed quite a bit. I came from a Pixel 3 that I was having to charge 1-2 times a day. My 4a I generally only charge once a day. Yesterday I ended the day with 4.5 hrs SOT, 17% battery remaining, after 26 hrs since I charged it. I've never had a phone with that battery life, but it was about the same as my old phone in the first few days. So give it time, you've got 14 days to return it. If by 12 days it's still bad, then consider returning it.
Between the 4a & 4a5G, the only differences are the CPU, display size, battery size, & 5G. If there's an issue, I'd say it would either be that the CPU isn't as efficient (which I'd doubt), or that 5G is draining the battery at a faster rate than the LTE/CDMA radios. And that's not uncommon. When Verizon introduced LTE, the first flagships that supported it had HORRIBLE battery life. Like charging 3-4 times a day in some cases. It took a few years before battery life was comparable to what 3G phones had. So it could just be that. I generally don't jump on new networks for a few years because it takes time for them to work the kinks out.