Bad Starter? Battery issues car won't start after sitting

[lummert]

Four weeks is not a long time for a car to sit.

[rgk]

Explain what happens when you try to start the car. Does your starter rotate as normal, or slow and sluggish?

[Fred760DC]

Battery. BAttery chargers report "fully charged" when the battery can take no more juice (amps) but a bad cell or two would keep it from turning over, even if the charger gauge says fully charged. Put a voltmeter on it and see if it reads 12Volts min.
2 AMPS PER HOUR OVER NIGHT IS 16 AMPS. Not much in a dead battery. Diehards are like 885cca, so 16 is less than that.
I'm glad you bought a charger, rather than rip off the retailer. Did it have instructions?
Solenoid. If the batery is too low to turn the car over you might still hear a loud click from the solenoid that throw the bendix gear to let the starter motor (electrical) engage the engine's flywheel. The starter is on the engine drivers side all the way to the rear down low. It's cylindrical, and has a whooping big wire leading to it. make sure the connection is tight. (Wiggle it with your hand.) It feeds the solenoid which clicks into place and feeds power to the electrical motor. It also moves a spring loaded gear gear into place between the starter motor and the flywheel because you can't have the starter engaged when the car engine is running. (That's that screeching noise we all hate) If you remember starting the car while it was running you could have fried the solenoid, (which is cheaper than a starter) and the starter won't get juice at all. Stuck solenoids often respond to a sharp rap with a heavy screw driver. Notice the drum the big wire goes into and thump it. While someone turn the key. If it starts don't replace the starter, just the solenoid. (It is ok to bang your head when leaning into a car to rap on a solenoid and it suddenly starts.)
Volvos will not start without oil pressure, which is a good idea, but often overlooked. Check it often and now.