Gym Overview and Strategy

• Once you hit level 5, you can choose a team and begin taking on gyms. Click here if you want the basics on how gyms work!
• Up to 20 gyms can be held at once by a single trainer.
• Pokemon can't be added to gyms when they are under attack.
• If a full gym (i.e., containing 6 Pokemon) is attacked and one Pokemon is knocked out, a trainer on the defending team will not be able to put more Pokemon in the gym until ~10 minutes have passed (from when the first one is knocked out, in the case of multiple Pokemon being knocked out).

• Counts as a daily stop bonus.
• You can spin a gym Pokestop using a GO plus just like a regular Pokestop.
• Spinning a gym gives 2–4 items, +1 bonus item if you are on the same team as the spun gym. More items are rewarded based on gym badge bonuses.
• If you do not have a regular raid pass in your inventory and have not obtained one for the day yet, spinning a gym will give you a raid pass.

• A trainer can be rewarded one coin every 10 minutes per Pokemon placed in a gym.
• Time defended does not round up, for example, a Pokemon placed in a gym for 19 minutes will net 1 coin.
• You can earn a maximum of 50 PokéCoins per day (you need to accumulate 8 hours and 20 minutes of total Gym defending time to be eligible for the 50 coins). If you have more than one Pokémon return from Gyms in a single day with more than 8 hours and 20 minutes of total defending time, the maximum bonus for the day is still limited to 50 PokéCoins.
• The PokeCoin reward limit resets at 12:00AM your local time, the same time as the daily streak bonus.
• PokeCoins are only awarded when your Pokemon is defeated and removed from a gym, and Pokecoins are not awarded retroactively (i.e., if you have only one Pokemon in a Gym, and it stays there for 3 days before being defeated, you'll earn 50 Pokecoins on the third day, but nothing for day 1 or 2).

• Every Pokémon on a Gym has motivation, a measurement of the Pokémon’s desire to defend the location.
• A Pokemon initially placed in a gym doesn't start with max motivation. An estimated 8-9% CP, 10% motivation is dropped upon placement.
• As a Pokémon loses motivation, its CP will temporarily decrease, making it weaker in battle.
• When a Pokémon’s motivation reaches zero, it leaves the Gym and returns to its Trainer the next time it loses a battle.
• Trainers from opposing teams battle to reduce the motivation of the Pokémon on the Gym.
  • Estimated: 27 - 28% motivation lost per battle.  This means it takes about 3 battles per Pokémon to fully defeat it.
  • A Pokémon with 0 motivation has 20% of its maximum CP.  For example, a 1,000 CP Pokémon will be kicked out after reduced to 200 CP.
  • A Pokémon with less than 20% motivation (36% of maximum CP) will have its CP shown in red and will likely be kicked out after one fight.
• Pokémon gradually lose motivation over time.
  • Estimated: 10% motivation lost per hour for Pokemon >2400 CP and CP_drop/hour = 4.975 * 1.001616 ^ (MaxCP) if < 2400 CP.

Many thanks to 0x00000000 for helping research Gym Motivation mechanics.

• Reinforce a friendly Gym by giving Berries to the Pokémon, increasing the Pokémon’s motivation and making it harder for rival teams to capture the location.
• You can only feed a max of 10 berries to a Pokemon in 30 minutes (the limit is tied to the Pokemon, so if a Pokemon is fed 10 berries in 3 minutes, but gets knocked out of the gym 5 minutes later, if the trainer heals it immediately and places it in another gym in a minute, it would then have ~21 minutes before it can accept more berries).
• Feeding a Pokemon multiple berries in succession reduces the amount of motivation gained per berry. For the first six berries, each one is less effective as the previous one; the 7th to the 10th one will be as effective as the 6th one. For the detailed sequence of berry effectiveness, you may visit this guide. There is a cool down of 30 minutes before this reduction resets.
• Remote feeding is as 25% effective as in-range feeding, except for Golden Razz Berry.
• Golden Razz Berry fully restores a Pokemon's motivation.
• Feeding any Pokemon ANY berry nets +20 stardust per berry fed.
• Feeding any Pokemon (ally's or your own Pokemon) any berry can possibly award one candy of that fed Pokemon. According to this TheSilphRoad research, the candy dropping rate is around 1.2% per berry fed.

Badges have four tiers: Basic, Bronze, Silver, and Gold. Badges will earn you bonus items when spinning the Photo Disc of the respective gym.

If your team controls the gym, you gain an additional item and XP is multiplied by 1.25 for 31, 63, 94 and 125 XP respectively for the various tiers of gym badge.

• Badge EXP from defending awarded when you get kicked from the gym.
• No EXP is awarded for spinning a stop.
• There no in-game method to track your exact badge progress beyond estimating by looking at the bar and knowing the badge EXP needed for each badge level.

Many thanks to 0x00000000 and  DrThod_PokemonGO for helping research gym badge mechanics.