Battle Points (BP) are one of in-game currencies.
Use[]
Battle Points can be used to purchase heroes, emblem chests, Power Crystals, draw in Emblem Matrix, and some other things. However, Battle Points cannot be used to purchase other in-game items such as skin and battle emotes. Battle Points cannot be converted to 
Diamonds and vice versa.
How to Obtain[]
Mainly, players can obtain Battle Points through playing Classic, Ranked, or any Arcade Mode matches. There are also other ways to collect Battle Points, such as selling unused items/trial cards from inventory, opening reward chests, seasonal rewards, watching ads, etc. Moreover, getting a hero that has already been purchased will convert them into Battle Points.
Battle Points Obtained from Methods:[]
Medal Chest: 200-250
Free Chest: 40-50
Playing Matches: 30-200
Selling (Trial Cards): 30 (1 day) 90 (3 days) 270 (7 days)
Season Rewards: 2000-10000 (Depends on rank by end of season)
Battle Points Limit[]
There is a weekly limit for Battle Points depending on player Credit Score. Battle Points limit can increase to + 1500 with the use of 
Double BP Card. Losing credit scores will reduce Battle Points limit but reclaiming the lost credit score will increase it again. Battle Points limit will refreshed every Monday 05:00:00 server time. As of patch 1.4.08, the maximum weekly Battle Points limit from matches is 10000 with the use of Double BP Card.
Trivia[]
Players above 100 credit score can earn +5% from matches, while players above 110 Credit Score can earn +10% from matches.
A Power Crystal is equivalent to 250.