NP-BK1 Lithium-Ion Battery - Rechargeable Ultra High Capacity (1100 mAh) - replacement for Sony NP-BK1 Battery Replacement battery for the Sony NP-BK1, Lithium-Ion (Li-ion) 3.7V (1100mAh) 100% compatible with your OEM battery - 3 year warranty. Made with high quality Japanese cells. Synergy Digital is a Registered Trademark