Plug (not maintenance-free as well as AGM-batteries)
WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.
On top of the battery is a cover with six plugs, one for each cell. The plugs can be opened when checking and topping up the electrolyte.