Mercury batteries were formerly commonly made in button sizes for watches, but due to careless disposal and the resulting mercury pollution hazard, they are no longer available. This is also a concern for users of vintage camera equipment, which typically used a mercury button battery in the exposure meter for its very steady voltage characteristic. Substitute non-mercury batteries have been produced to replace certain discontinued mercury batteries, typically by incorporating a miniature voltage regulator to simulate the flat voltage discharge characteristics of the original batteries.