Season 1

Season 1 of GO Battle League lasts from March, 2020 to May , 2020. It is preceded by Preseason and succeeded by Season 2.

Formats

 * Battle League Great.png Great League: March, 2020 to March , 2020
 * Battle League Ultra.png Ultra League: March, 2020 to April , 2020
 * Battle League Master.png Master League: April, 2020 to April , 2020
 * GO Battle League.png All three Leagues: April, 2020 to May , 2020

Ranks and Ratings
The requirements are different from Preseason.

Rewards
Basic Premium

The random items include:
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Reaching rank 10 can earn avatar items and an avatar pose inspired by Steven.

Pokémon
Metagross is the first guaranteed encounter. Pikachu Libre is the first encounter in rank 10, one only.

Certain Legendary Pokémon or Mythical Pokémon can be obtained starting at rank 4 during their time in tier 5 Raid Battle.

End-of-season rewards

 * (rank 7 or above)

Events

 * GO Battle League Season 1 Launch Celebration was held to promote Season 1.
 * When Season 1 was initiated, the rank and rating of Trainers were slightly altered from that in Preseason. Later, Niantic adjusted all Trainers to rank 1. If a Trainer claimed the end-of-preseason rewards during this time slot, their Preseason record would be lost.
 * Due to coronavirus outbreak, trainers do not require walking or PokéCoins to unlock battle sets since the start of Season 1 to May, the end of Season 1.
 * It was originally planned to end on April.
 * Since April, if one loses all 5 matches in a set, they can continue playing in that same set until scoring a win for up to 15 losses, after which they will move to the next set.
 * GO Battle Day: Marill takes place on April, 11 a.m. to 2 p.m. local time. Marill will appear as a guaranteed Basic Reward after the first and third wins, or after every win if using a Premium Battle Pass. Trainers will also receive double Catch Stardust for catching Marill during this time period.
 * For the whole day, Trainers can complete 20 sets of battles.
 * Season 1 was originally planned to end on May, but due to certain technical issues, it was delayed until May.

Maintenance

 * March, 2020 - soon after the start of Season 1, GO Battle League was closed for 20 minutes to adjust rank and rating
 * On the same day, it was down for 3 to 5 hours again.
 * March, 2020 - temporarily closed for 1 to 3 hours
 * March, 2020 - temporarily closed for 1 to 3 hours when Great League ended
 * March, 2020 - temporarily closed for 1 to 3 hours
 * April, 2020 - temporarily closed for 1 to 3 hours
 * April, 2020 - temporarily closed for 1 to 3 hours
 * April, 2020 - temporarily closed for 1 to 3 hours when Ultra League ended
 * April, 2020 - temporarily closed for 3 to 5 hours
 * April, 2020 - temporarily closed for 3 to 5 hours
 * April, 2020 - temporarily closed for 2 to 4 hours
 * April, 2020 - temporarily closed for 1 to 2 hours
 * May, 2020 - temporarily closed for 2 hours
 * May, 2020 - temporarily closed for 5 hours
 * May, 2020 - temporarily closed for 3 hours