On recent monthly detailed maintenance check I discovered a crack on the top of a P4A battery. The crack was on the top where the two thumb locks are. These are screwed on to the actual battery cell. The cracks are starting from the plastic injection mold dimples. Out of 4 batteries, all three are doing it, with one worse than others. These do not affect the fit into the battery compartment or the function of the battery itself. I contacted DJI and my batteries were our of warranty. I asked if I could buy just the tops and was told No, replace the batteries. Purely a manufacturing defect. A little superglue has stopped the spread and I will continue to monitor. Again, very small cracks not affecting the attachment to the drone or the battery cells themselves.