Volvo Repair: No contact at all, volvo xc, voltage value

Question
Volvo XC AWD 1998

There is nothing working no electric power at all.
No contact, can't even lock the doors.
3 days ago, could not start the car but at least there was a certain contact and the instrument were working in the dash. Brought it to the garage change the spark plug and dried the plugs because of damptness. Now there isn't a sound coming out of the car:DEAD. They say it could be the battery.We tried to boost the battery "nothing". Could it be the alternator.what could be the problem.
Thank you for your help.

Answer
Hello,
try the car with another battery or jump-start the car with another battery. If the problem is battery problem, you will hear a noise while you are starting like "theerrrtt".
If you did not hear any noise while starting, it means there can be a problem regarding "starter motor", check its cables, maybe one of them is damaged.
Also, please check the ground connection of battery, it may have problem.
For battery, its voltage value should be 12,5 Volts or more while the engine does not run, while the engine runs, the voltage level is alternator level it should be approximately 13,9 Volts or more.

Regards...