Wrong/bad/dumb way.
RIGHT WAY
Ensure battery is fully charged.
Load test battery to make sure it's good.
Install battery in car with good clean connections.
Inspect alt., belt, mounts, wiring and regulator. Fix as needed.
Perform starting draw test.
Fix as needed.
Start car and do a charging system test with a heavy load tester.
Fix as needed.

That's why people do the disconnect thing. It's quick and easy. It does NOT check all the components and circuits like you should, and it can cause damage.