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các ranh giới đánh dấu sự kết thúc của miền một trong nhà cung cấp dịch vụ di động và bắt đầu khác là vô hình. Trừ khi bạn đã đi du lịch các tuyến đường trước khi, bạn không thể biết được bạn đã rời khỏi khu vực nhà của bạn và nhập khác. Nhưng điện thoại của bạn có thể. Một trong những chỉ số trên | The Cellular Connection A Guide to Cellular Telephones Fourth Edition. Robert A. Steuernagel Copyright 2000 John Wiley Sons Inc. ISBNs 0-471-31652-0 Paper 0-471-20340-8 Electronic 9 OPTIONS AND ACCESSORIES Cellular telephones have so many features built into them that it s difficult to think of anything more that could be added to them. Many of these features have been discussed in previous chapters but we will explore them further here. BATTERIES A second battery is perhaps the most-requested accessory of any portable cellphone user. It extends the time between charges while on the road and ensures that there is always a charged battery at hand if you find that the battery in your phone is dead. Since the standard battery is usually a nickel - cadmium NiCad battery users often will purchase a second battery for more performance rather than just as a spare and get a nickel-metal hydride NiMH or lithium-ion battery. Note that some types of chargers require that the battery is installed in the phone while it is charged. This means that you can t use the phone while it is charging. CHARGERS AND ELIMINATORS Battery chargers may be trickle chargers or rapid chargers. Rapid chargers are more expensive and charge the battery faster. Travel 87 88 OPTIONS AND ACCESSORIES Popular accessories include a case extra battery battery charger and battery eliminator for the car. Photo courtesy of Nokia. chargers are small trickle chargers made to take up less room on trips. Some premium chargers may charge several batteries at once and serve as a convenient cradle for the phone at home or office charging one battery while it is installed in the phone. An important issue for portable users is battery life so a battery eliminator is an attractive accessory. The battery eliminator plugs into the cigarette lighter of a vehicle and substitutes for the battery. Most also charge the phone s battery at the same time. HANDS-FREE OPERATION When you were learning to drive you were told to keep
