Mi mobile batteries are rechargeable Lithium-ion or Lithium Polymer units designed specifically for various Xiaomi, Redmi, and POCO phone models, with capacities typically ranging from 2,000 mAh to over 5,000 mAh. They are available as replacements for older, degraded batteries and should be matched to the specific model number (e.g., BN46, BM4E) of your device.