Nickel Metal Hydride batteries--my favorite!

Answer in the comments: why haven't disposable alkaline batteries been outlawed? Since we throw most of them into our trash cans, they will almost certainly end up in landfills where their metal casings will slowly corrode away after being exposed to water, and the electrolyte within will be released into the environment. A good portion of it will likely be picked up by the landfill's leachate collection system and be broken down at a water treatment plant, but still!