ON-VEHICLE BATTERY SYSTEM

PROBLEM TO BE SOLVED: To enable easy handling when a power storage part is separated from a lead storage battery in an on-vehicle battery system having the lead storage battery and the power storage part attached to the lead storage battery.SOLUTION: An on-vehicle battery system 100 according to one embodiment includes: a first power storage module 10; and a second power storage module 20 located adjacent to the first power storage module 10. The first power storage module 10 includes a lead storage battery and a first housing 14 which houses the lead storage battery. The second power storage module 20 has a power storage part having energy density higher than the lead storage battery and a second housing 24 which houses the power storage part. When the second housing 24 is installed so as to be attached to the first housing 14, a spring 98 biases a pin 97 toward an exterior terminal 96 thereby causing the pin 97 to contact with the external terminal 96. Consequently, a contact terminal 95 electrically connects with the external terminal 96. When the second housing 24 is removed from the first housing 14, the pin 97 does not contact with the external terminal 96 and thus electrical connection between the contact terminal 95 and the external terminal 96 is interrupted.