If you use your PDA for long periods of time with no way to plug into a power outlet, you'll want an extra battery. You simply remove the spent battery and install the fresh one. Many people use an extra battery when on long flights. If you listen to MP3's and play games continueouly, you'll want to purchase an extra.

Model Name: EA-BL06 Dimensions: 35.3mm x 53.1mm x7.1mm Weight: Approx. 27.5g Features: • Same as bundled battery pack • Rechargeable Lithium-ion    Battery 3.7V, 950mAh