I’m not sure what X and XI mean. There are ATTb/i (not video) and ATTxb/i (video capable).
Credits (premium) are on accounts, not cameras. Did you set up two different accounts, one for each camera? I’m running 25 cameras (give or take) on one account so the cameras pull from a pool of credits. I don’t have credits for each camera.
You are aware that lithium batteries go from full power to no power with little, if any, warning? You will see P5 until the camera stops.
I use 1 year/4 G/$75 (not auto renew) on ALL my AT&T cameras, including a bunch that are running photo + video. The 90 day/2 GB/$25 plan might work for you. The 1 year plan might if this is your high traffic time of year and things slack off for a good part of the year. I’m confused, but maybe you have one camera on a one-year plan and the other on a 30-day auto-renew plan?
You must be getting a TON of pics! Some of my ATTb/i haven’t even used 100 MB of data in almost a year. I have one ATTx that has used under 2 G in almost a year. Granted, they are in low traffic areas, but the ATTx that has used the most data got a lot of traffic during timber thinning and I requested a bunch of videos.
I hope someone else will have some suggestions for you.