I saw these Canon CBK4-300 Rechargeable Battery in Amazon site and its the first time I saw Canon rechargeable AA batteries. They have 2500 mAh capacity rating and comes along with charger which has charge indicator light lets you know when your batteries are fully recharged.
The Canon CBK4-300 AA Rechargeable batteries and charger kit is designed to work with any Canon digital camera that's powered by AA batteries. This charger kit comes with four AA rechargeable batteries powered by Nickel Metal-Hydride technology that's free of the frustrating "memory" effect. Although designed by Canon for use in Canon cameras, these batteries will work in any electronic device powered by AA batteries.
What is wonder is Canon is not a battery manufacturer or not known for that. So these must be NiMH cells are simply re-labeled from other vendor ? But my opinion is even if Canon wouldn't re-label batteries from other members without thoroughly testing those. They wouldn't want to ruin their brand name by promoting low quality rechargeable Batteries. So I believe these Canon CBK4-300 Rechargeable Batteries are a quality product. You have plenty of good reviews about these in Amazon with high ratings. Even at Amazon these Canon CBK4-300 Rechargeable Batteries are sold by Canon itself.