Now that think about it there was some remark I read about the dual illumination types that are based on a tritium dot fading out under certain lighting conditions. So the battery powered models may be better. Also tritium does have a half life
But I am not sure how important it is. But once the tritium is sufficiently degraded, it likely is not practical to fix or renew it.Tritium is radioactive and has a half-life of about 12.5 years, which means that half of the radioactive atoms will decay naturally in that time. Although tritium can be a gas under controlled conditions, its most common form is liquid, because, like hydrogen, tritium reacts with oxygen to form water.