Dead Battery. Are you sure your battery can maintain or hold a charge?
700 to 740 MegaBytes
Most of the 91 volvo's airbags were not standard. However you can take it to any volvo dealership and have them add if you do not already have them.
pull out ashtray and lighter- realys are behind ashtray
With new oil filter, four quarts.
They may still be available from your Volvo dealer. There is no charge for them.
The Russian 91-91 in caliber 9x39 uses a 20 round box magazine,
http://www.brickboard.com/FAQ/700-900/ElectricalCircuitsRelays.htm#RelayLocations
You need to replace it. There are 2 screws that hold it on.
Batteries charge nothing they hold a charge.
4 quarts
Depends on the condition of the battery. Most will hold a charge for at least 6 months if they are not connected to anything.