The BL-4CT is a 3.7V lithium-ion battery commonly used in older Nokia phones, such as the Nokia 5630 XpressMusic and Nokia 5310 XpressMusic. It's known for its relatively compact size and moderate capacity, typically around 1020mAh, which offers a decent battery life for those devices.

If you're looking for a replacement or spare, it's important to ensure that the battery you choose matches these specifications. Some third-party manufacturers may offer compatible versions, but it's often best to go with genuine or high-quality brands to ensure optimal performance and safety.

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