The length of camera flash life varies depending on the brand that you are using. A camera flash that is loaded with fresh batteries will perform better than one with depleted batteries. More expensive flashes typically have a longer lifespan than cheaper versions. If you are shooting with flash it's always a good idea to replace batteries before your shoot so that your lights are performing at their best.  It’s worth noting that you shouldn’t put old camera flashes on modern cameras. Without going too deeply into the science of it, you can destroy your camera if you attach the wrong kind of old speedlight to it. This typically only applies to flashes from decades ago.