The IRAY-AC37 Bolt series battery extender enhances the operational longevity of your Bolt series thermal optics by enabling the use of an 18650 battery in place of the standard 18500 battery. This upgrade extends battery life by over 75%, providing prolonged usage in the field. Compatible with models such as Bolt TL35, TL35V2, TH35C, TH50C, TH50CV2 and TD50L (excluding BOLT SE series), the IRAY-AC37 is specifically designed for flat-top 18650 batteries. It does not support button-top 18650 batteries due to its unique threading requirements.