Season 1

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

Ranks and Ratings
The requirements were different from Preseason.

Rewards
Basic Premium

Stardust

The random items can include:
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Reaching rank 10 awarded avatar items and an avatar pose inspired by Steven Stone from Pokémon Omega Ruby and Alpha Sapphire.

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

Tier 5 Raid Bosses could be obtained starting at rank 4 during their time in raids.

These Pokémon were released with the start of the Season:

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 the COVID-19 pandemic, Trainers do not require walking or PokéCoins to unlock battle sets since the start of Season 1.
 * It was originally planned to end on April and then May . The bonus is still active for today.
 * Since April, if one lost all 5 matches in a set, they could continue playing in that same set until scoring a win for up to 15 losses, after which they would move to the next set.
 * This feature was removed at the beginning of Season 3.
 * GO Battle Day: Marill took place on April.
 * 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