BATTERY CHARGER CAPABLE OF EFFICIENTLY COOLING SECONDARY BATTERY IN BATTERY PACK AND CHARGING CIRCUIT UNIT IN BATTERY CHARGER

A battery charger that is configured to charge a battery pack including a secondary battery includes: a housing; and a charging circuit unit disposed in the housing. The housing defines a first air passage in which air flows to cool the secondary battery and a second air passage in which air flows to cool the charging circuit unit. The second air passage is independent from the first air passage.