Never have any problem myself. The Canon 7D batteries last for about 800 exposures and have a pretty accurate indication of the amount of charge in them. The Pentax runs on AA batteries. Standard batteries are fine, but if using the rechargeables make sure they are type which retain a high percentage of charge for a significant time if unused. It's well worth paying the extra over what standard rechargeables cost.
Batteries, and the cameras using them (in terms of having power), are significantly better than those of the last forty years that used button cells of various types. They were a real pain, and continue to be so as the more modern cells are often not of the correct voltage.