An intelligent charger with a diagnostic function and a charging method. The intelligent charger includes a control module, a diagnosis module, a charging module, a multi-path switch and a detection module. The control module is sequentially connected to the diagnosis module, the charging module and the multi-path switch; and the detection module is sequentially connected to an external connection terminal of a battery, the multi-path switch and the fault diagnosis module. The charging method includes a charging mode and a diagnosis mode; the diagnosis mode includes a two part function, namely fault diagnosis and lifetime detection; the fault diagnosis is detecting a fault problem which can occur in the battery and providing a prompt; and the lifetime detection is detecting the current capacity of a battery, and determining current battery life through the ratio of current capacity to rated capacity.