If you truly want the answer, get a digital food scale and weigh time to time. In my experience, bats do gain/lose weight (up to 1 oz). Also depends on where your bats are coming from, and what the humidity level of the origin is relative to yours - this is why any bat I get from the Uk, drops 1-1.5oz here in North America (houses are drier due to heating during winters), whereas Indian bats don’t show much change. Also, a bat that is newly manufactured, will have more moisture to lose than something that’s been sitting on the shelf for a year.
Get a scale and track the changes - going by feel isn’t enough as the same weight can feel lighter/heavier on different days.