I'm a little confused about Google Voice. I briefly tried a phone thing with Google but it was several years ago and it was VoIP, which would require an internet connection (I used it on my computer). I just briefly looked up Google Voice on Wikipedia and it sounds like it's different; from what I read, it's used with an existing phone line. Right now I honestly can't see the point behind that; if you have to pay for a phone line why not just use that, especially if you're not on a landline? But as I said, I don't know much about it.
The rates you quote, $35 and $45, are what Straight Talk charges; is that your provider? I'm familiar with Straight Talk - I've had it for several years, just switched from a dumb phone to a smartphone - and I can tell you Straight Talk's $45 plan has unlimited talk and text, which would beat whatever Google's limit is (although 750 seems really, really high to me; do you really send that many texts a day?). The $45 plan also has a monthly data cap of 3 gigs, and while it's called "unlimited" it isn't really - it does not allow tethering or streaming, if that's a consideration. But for that money, whether it's $35 or $45, you'd have a reliable phone line in addition to the Google Voice.
I don't really understand what the other reply said about WIFI and Xfinity; I've never used Xfinity. If there is any VoIP still around you could use that with public WIFI and then you wouldn't even need a plan for your phone, but you'd have to stay close to a hotspot.
I'm not familiar with Republic Wireless, which makes me think they're not in my area. If you decide to check out other plans make sure that whatever towers they use are near where you are (Straight Talk uses Verizon, T-Mobile, and AT&T, and maybe even Sprint; it depends on the phone).
About charging - you are correct, smartphones are battery hogs; most of the people I've asked about this say they have to charge their phones every day, sometimes more than once a day. I leave mine plugged in as much as possible - to the computer when I'm using it (ie, now) and to the wall during the night. I also have a solar charger but it has been less than efficient with both my dumb phone and my smartphone. But solar chargers differ; yours might be better than mine.
You might also be able to find a public place with wall outlets; so many people have smartphones now that a lot more places are adding these. I've seen them at big city train stations and I suspect libraries might also have them; again, it depends on your location.
I'm not sure if that helps; as I said, I'm out of touch with what's available these days. But maybe it will help you make your decision.