A battery pack includes a pack body that includes a battery cell and that has an external shape substantially symmetric with respect to the horizontal and vertical axes, viewed from a front face on which terminals are arranged, and a terminal unit on the front face. The notification architecture includes a notification process, configured for receiving notification messages for respective subscribers from messaging sources according to a prescribed open protocol such as Internet Protocol. At least one second contact within the housing extends through the housing wall for a second electrical connection. A second strut member also having joined outer walls defining an inner cavity extends from a first end to a second end. The web service platform implements the on-demand message handling service’s threads to perform background processing on the received client message.