I have a 3 year old Dell Studio, it works fine with battery power or with AC power ( only when battery is taken out), but doesn't charge battery or work on AC power with battery in place. Tried replacing with a new battery and still the same problem. Tried changing the adapter and still no luck.
When a system is plugged in and unplugged several times a day, it may reduce the life of the battery. When the longevity mode setting is enabled, it protects the battery from frequent charge and discharge cycles. The battery only charges between 88%-100% when longevity mode is enabled.