This CTA Digital battery replaces the Casio NP-20 battery. This battery was designed to meet or exceed OEM specifications and is 100-percent compatible to the original equipment chargers. Chemistry: Lithium-Ion - Capacity: 630mAh Voltage: 3.7V - Warranty: 3 years

Amazon.com

The CTA DB-NP20 Replacement Battery is designed to replace the Casio NP-20 battery. The CTA DB-NP20 is a high-capacity rechargeable Lithium-ion battery that ensures maximum battery life and maximum power. This CTA battery features No Memory Effect, which lets you recharge the battery when it is only partially drained without reducing the battery's long-term performance. This 3.7-volt battery has a power output of 630 mAh, and comes with a manufacturer's limited three-year warranty.