I only used the 630g for about 5 months a few years ago. But I can say the 670g was getting between 2 wks and 10 days on a single battery. This depends on how far you are willing to let it go down. I tend to change mine within a day or so if getting to yellow.
Using the sensor will deplete the battery quicker so if you are not using the battery you will get greater use.
I have heard of non sensor users getting 3-4 weeks but again I think that depends how far you are willing to let it go into yellow. (Running out of power is one of my obsessions so I change quickly, hey we all have our thing).
If you are getting less than 10 days in a new battery I would call Medtronic. They may advise trying a different battery. I use energizer alkaline batteries.
This is the purchase option I use fir batteries.
Energizer Max AA Batteries & AAA Batteries Combo Pack, 24 AA and 24 AAA (48 Count) https://www.amazon.com/dp/B087GMJXMC/ref=cm_sw_r_cp_api_glc_fabc_hKl5Fb3G6YEGX
( I will add my disclaimer when I get to a computer. Suffice it to say that I am a medtronic ambassador - they gave me a cool shirt but I don’t get paid - my thoughts are my own - I use medtronic products but like you I pay full price( blah blah blah