Abnormal power usage?

We installed a Mayfly out at the border of a forest/marsh last week and everything went fine. I tested our loggers in our University’s greenhouse and it seemed like our batteries/solar panels were working just well. However, in the field, one of our loggers pretty much ran out of juice within the span of like an hour. We ended up replacing it with an entirely new logger just so we can troubleshoot the problem and it works just fine so the solar panel can’t be the problem, so now I’m a bit confused as to what could cause the voltage to drop so rapidly. Perhaps a battery issue? Or maybe the sensor was somehow operating constantly so it just drained really quickly.