The Oakley 1100mah Firefly battery is perfect for those who prefer a long lasting battery. The battery itself is about the size of a small cigar. Each battery, fully charged, is good for approximately 6-12 hours (depending on use) and takes from 3-4 hours to charge. Around the bottom is an LED indicator light that lets you know the charge level on your battery. Green is a full charge, yellow is a medium charge, red is a low charge. When the battery is off, the bottom functions as a small flashlight. Compatible with eGo chargers and atomizers. Available only in Purple.