Battery life is strictly a function of use. It is always possible that there is some sort of mouse problem.
I have used rechargeables for several years. I currently use 2400 mAh Energizers and a 15 minute charger - also Energizer. I bought a bunch of batteries and the charger (new) on eBay at a very reasonable cost.
In addition to reducing cost over time, the rechargeables are environmentally friendly.