The types sold at hardware stores can only hold 50 to 70 percent of the energy in a regular alkaline battery. You will have to change batteries more often. Also, if you keep recharging them before they are spent, they will not live very long. The batteries will lose their charge over time so do not use them in low-use appliances, such as smoke detectors. Some toys use the batteries so fast a rechargeable battery cannot keep up, but generally you can use them anywhere else.
Good uses are flashlights, radios, photo flashes, handheld games, beepers, etc.
My beeper has been solar powered for years. Do not put batteries of different brands together. They will not work as well since they are slightly different. Batteries and chargers are sold at Radio Shack, Meijer, and most hardware stores.