Serfas RB-LI4+ Battery The industry's most technologically advanced safety lights All lights are robs compliant and all testing is done in house More efficient leds & high quality lenses to increase brightness & Clarity Replacement LI-Ion battery for Serfas True 1000+ and True 1500+ Headlights Compatible with Serfas True 1000+ (plus) and True 1500+ (plus) headlights Easy to install and easy to charge