Once the battery starts to dim, it's best to put it away and get the backup light. Continuing to use it with a low battery shortens the future run time and will prevent it from obtaining a full charge.

My UltraStinger bulbs die a couple times a year per light. Then it's a short trip to the Streamlight factory service dept. for a free fixup. I have two Ultra Stingers and keep a Strion for a backup in my bag.