These 100mAh batteries are the perfect size, weight and shape for the Estes Proto-X / Hubsan Q4 nano quadcopter. They also feature the right connector to make them plug-and-play compatible with the Proto-X - that's right, this battery is designed to plug directly into the quad's main board - no soldering or adapters required. Also, the canopy will fit the same way it does with your stock battery! These batteries also feature built-in overcharge and overdischarge protection circuits to keep them in optimum condition flight after flight.