that certainly is completely typical with any rechargeable battery that is in its dying days. Battery quality can be a real factor here. I have had camera batteries bought at the same time and used pretty much the same, usage, cycles, recharging, yet the aftermarket one that cost half of the Nikon one has shown this sort of behaviour yet the orig. one doesnt--same life and usage, so it shows there is clearly a quality issue here.

also too, rechargeable batteries have a given lifespan and that lifespan is affected by many factors as well, how often used, total discharge, charging all the time and maybe not having a trickle charge function built into the charger....all kinds of factors, how hot the battery gets....