I’m usually pretty good about plugging in the phone to charge overnight when it’s low, but sooner or later it happens to everybody where the battery is running low while on the road. A car charger is a mandatory accessory for the wireless roadwarrior. It plugs into the cigarette lighter (now in this anti-smoker age usually referred to neutrally as power adapter) of the car to provide power during a conversation, or deliver a rapid charge to the battery.
Instead of paying a premium price to get the Sony Ericsson branded version from the AT&T store ($30 plus tax), I purchased a generic one from ebay for $1 plus shipping. It has an LED indicator, charges the battery fast but does not overcharge it, and is brandnew. Looks the same, works the same – good enough for me.