What version of Mayfly board do you have? And what brand of cellular board? There are a lot of combinations of hardware on EnviroDIY stations, and some are much more efficient than others. Also, do you have a spare Lipo battery that you can fully charge separately in your office and then put it into the station? If your logger is only working when there’s sunlight, then it’s pretty likely that your battery is faulty and won’t charge, that’s why it’s not providing power overnight.