... voltage indicationg. Applicable to versatile adapters (FC, ST, SC, LC)h. Handheld, large LCD backlight display, easy-to-use3. Specifications Wavelength range ... pcs AA batteries (lithium battery is optional)Battery working duration(h)No less than 75 (according to battery volume)Auto power ... need, and we can give you a proper price. ST800K Handheld Optical Power Meter