I purchased this light and a new Register II helmet. It fits the rear vent of the older Register but not the Register II. Luckily I still have the old helmet and it works well with that. It uses CR2024 coin cell batteries.
Love how it fits perfectly in my helmet. Probably not bright enough for your only blinky but the best backup light I've found.
This is an awesome addition to the Giro Helmet. Perfect fit and a great safety add on.
