Now that you know how to get strong(er) pokemon, you want to claim gyms with them. Let’s look at this gym that is claimed by a competing team.
You can see that this is a Iv13 gym, this means that it has room for three pokemon. You also see that the strongest pokemon, that of the gym leader (marked with a crown) is at CP830 and that this gym’s prestige is at 6000/8000.
6000/8000 means that if they train this gym enough to get the prestige to 8000, the gym will level up to level 4 and then it has space for 4 pokemon (with a maximum of Ivl 10).
In order for you to remove them from the gym you need to remove 6000 prestige.
IIRC you remove 1000 prestige per pokemon you beat and you remove another 500 bonus prestige for beating every pokemon without losing in one match.
So if you don’t have a pokemon strong enough to beat this Snorlax, you can still seriously diminish this gyms defence. By defeating the two pokemon prior to Snorlax, you remove 2000 prestige.
Also, don’t forget that you have 6 pokemon to beat the gym with vs. whatever level the gym is, so in this case 3 pokemon (it could be 10 pokemon if the gym is Ivl 10). So in short: 6 mediocre pokemon can beat 1 strong pokemon.
If we continue the example from above then you have 6 pokemon to defeat three pokemon. You will have to do this twice, since 4000-2000 (not considering the win bonus) = 2000.
After which you can claim the gym.
When you claim a gym it starts out with 2000 prestige effectively making the gym Ivl 2 and at Iv’ 2 it has space for two pokemon.
If you’re playing with someone else on your team or you know that people from your team are active in the area, then don’t immediately place your strongest pokemon on that gym.
Place a beatable pokemon on the gym, something around CP500.
This way you (or others from your team) can train and increase the gym level.
When training you’ll have to choose 1 pokemon. So choose wisely. You don’t have 5 backup pokemon to help you out.
Another difference between training and battling an opponent’s gym is that your pokemon can’t faint when training, whereas when battling an opponent’s gym, your pokemon can faint.
Every time you beat the pokemon that’s already on the friendly gym, the gym get’s prestige. How much depends on a number of factors, but it seems you gain more prestige for the gym if you beat it with a pokemon that has a lower CP than the pokemon that’s placed on the gym. The more pokemon you beat, the more prestige you gain for your gym. So even if you can only beat one pokemon and loose to the next pokemon on the gym, you still gain prestige for the gym.
The prestige requirement for the gym levels doubles every time.
Lvl 2 = 2000 prestige (starting point)
Lvl 3 = 4000 prestige
Lvl 4 = 8000 prestige
Lvl 5 = 16000 prestige
When the gym has the Ivl or prestige of your liking, you (or a team mate) can now place the strongest available pokemon.
After you’ve placed all the pokemon you wanted to place on all the gyms in the area (you can only place one pokemon per gym), you can collect your defenders bonus in the shop.
The button will say how many pokemon you’ve placed and will give you stardust and golden coins depending on how many pokemon you’ve placed. But be sure to press this button only after you’ve
placed all the pokemon you’ve wanted to place, since you can only press it once every 21 hrs.
If you take a look at your pokemon list, you’ll also see a gym icon at every pokemon you’ve placed. When that pokemon is knocked off the gym it will return with 1 HP. So you don’t lose your pokemon, you lend them to the gym.
In short, the only way your pokemon can faint, is when you’re trying to defeat an opponent’s gym.
If a gym is at max level and is full, you can still place your pokemon if it’s stronger than the weakest pokemon on that gym. The weakest will return to its owner.
Fun fact: if your pokemon is the one that made the attacker lose it will say `Battles won: X’ beneath him in the gym overview screen.
Credit: Imgur User LMG89