How to charge the CAIRE Freestyle Comfort from a wall outlet or motor vehicle?

The CAIRE Freestyle Comfort is a battery-compatible portable oxygen concentrator. There are two types of batteries available for the Comfort. First, the 8-cell battery also known as the standard battery can run for 4 hours on a setting of 2. Second, the 16-cell battery also known as the extended battery can run for about 8 hours on a setting of 2.