I always kept my P2 batteries fully charged so I would be ready to fly when the mood hit me, thinking the same way as you . One battery was fully bad and replaced (under 30 day return period) with only 17 flights on it. All 5 batteries suffered some damage, puffed up physically, and would suddenly drop from about 50% charge in a short time so I couldn't trust them for long flights. The batteries only have about 40 flights each on them so it dropped battery life from 300 flights (DJI specs) to less than 40, losing about $111 per battery ($129 price for P2 batteries). I realize that the batteries probably would not have lasted for 300 flights as DJI states but I used their number.
I am meticulous now with the P3 batteries, store them at about 45% charge and don't charge them until ready to fly. The inconvenience of having to charge before flying is more than offset by having batteries I can trust. I won't know for a while if it helped enough to be worth the bother as I haven't used it much so far, still just starting the break-in of 10 flights for 3 batteries as recommended on another thread. Because DJI added the auto discharge feature I assume it was a serious problem with the previous batteries.