Volvo VNL 780 Operator's Manual page 452

442 MAINTENANCE AND LUBRICATION
The VHD vehicle has two styles of battery boxes available. One is covered with a plastic
cover, the other cover is made of chromed diamond plated steel.
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There may be up to four batteries installed. Always make sure the batteries are fastened
properly in the box.
When disconnecting battery terminals, always disconnect the engine ECU fuse(s) first, then
the ECU ground wire(s), then the main ground cable, and finally the main positive cable.
Reverse this order when reconnecting the cables and wires.