My Opel Astra won't start after changing the alternator

Hi everyone, after replacing the alternator, and the battery, although new, discharged and hasn't been used for at least 5 months, I was given a portable jump starter. I connected it to the battery terminals, the dashboard lit up and it tried to start the car, but it didn't.
My question is, do I need to fully charge the battery?

Hi, you should try it with a fully charged battery to rule out the battery as the problem. Let me know how it goes

Hi mate, from what you've said, you've had the car battery connected for five months without using it. Whenever you don't use the car for that long, the battery is usually removed or the cables disconnected. It's possible the starter brushes have seized up and are stuck to the armature. Try tapping the starter with a hammer when someone else tries to start it, but not hard enough to hammer nails. Good luck. Cheers

Hey mate, where are the starter brushes? As you can see, I'm a real klutz.
Thanks.

You can try tapping the starter motor (gently, so you don't damage anything) to loosen the brushes, but I doubt they're stuck. It's more likely the battery is weak; you should try another one. Cheers