There are a number of problems out there when creating wireless devices. Everybody faces them, and they apply to just about every type of wireless device. Battery life, recharging time, weight, construction, range. And unfortunately, they don’t always get solved. If it’s not a built in rechargeable battery, then you’re running through AAs or AAAs fairly fast. IF the device does have a built-in battery, it might take a while to charge, or doesn’t hold that charge for long enough to be effective.