A battery assembly has a battery case and a battery acid container, wherein the battery case has a number of sockets on an upper central part thereof and the battery acid container has a number of adjacent vessels. Each socket has a central post with crossed bridge linked therebetween to form apertures that surround the central post. Each vessel has a neck with a hat-like plug for inserting into the opening of the neck and an air vent between every two adjacent vessels. The hat-like plug has a weak portion which is easily torn apart upon insertion in the socket to fill battery acid therethrough and a reinforced portion for retaining the torn part affixed to the plug. A cover has a number of annular plugs to seal the sockets.
