Features:

• Replacement battery for the Casio EX-S1, M1, S2, M2 cameras
• Lithium ion chemistry free from memory effect
• 3.7 volts
• 630 mAh power rating
• Great as a backup battery

Editor Reviews:

Product Description:
Designated extra or replacement battery for CASIO EX series Digital Cameras / Rechargeable lithium-ion design

Rating : - An easy fix for the NP-20
My NP 20 gave me the flashing red light of death and I got Casio to replace it. Then I had the same problem with my second NP 20 so I dug around for a way to fix it and I found the following advice on a site called FixYa. It worked instantly and I didn't risk ruining my battery.
ylu1 writes:
I had the same problem as this.
what i did was...
i kept putting the battery on the charger then took it off as soon as the red light came on.
i did this about 6 times.
doing this puts a bit of charge in the battery each time before the charger starts to flash.
after the battery as got enough charge in it it can start to charge.
hope this helps.