How old are the packs? And how do you store them? They degrade with age, how they are stored makes a significant difference. Storing fully charged and/or at warm temperatures is hard on them for example.

At the risk of going off subject a little, have the motor temps increased any? The rotors lose some magnetism with age, worst if ran hot, will then run hotter and with less efficiency.

Of course always make sure the car is running smooth, bearings aren't getting gritty, etc.