Tower XP (BTDB2)

Tower XP is experience points for towers. They are separate for each tower. In Bloons TD Battles 2, players start with 2-2-2 (2-0-0 prior to 1.0.2) for all towers when bought, but all upgrades at least Tier 3 must be unlocked with XP. Unlike Bloons TD Battles 1, which unlocks upgrades purely by tier, each separate upgrade has their own XP requirements. Each bought tower starts with 150 XP.

Whenever ending a game, the rewarded Tower XP is split evenly by percentage. XP is also gained further as rounds go. Winning earns roughly 100% more XP than losing. As a general rule of thumb, players earn a minimum of 400 Tower XP for wins and 200 Tower XP for losses, and this increases with rounds passed, with an average of 1000 XP for wins and 500 XP for losses in mid-game, and 1600 XP and 800 XP for wins and losses in late-game. There is no known formula as of yet, but for now this is just the general rule of thumb. However, losing before Round 6 earns 50% less XP than normal.

Once all upgrades have been unlocked for an individual tower players can begin unlocking Monkey Mastery for that tower, which gives various cosmetics related to that tower.

Earning XP
Tower XP is earned by passing rounds in a game. Total earned Tower XP is split into each tower by ratio of money spent on them. The base amount for rewarded Tower XP is increased by a small percentage for playing on higher arenas, starting from White Wasteland (+5%), Lead Dungeon (+8%), Ceramic Crucible (+10%), and MOAB Pit and beyond (+15%).

Players earn a certain amount of XP per game, plus bonuses such as VIP's 3x Tower XP bonus (technically +200%) or the 2x XP Boosters (technically +100%). At the end of the match, the player can choose to gain more XP from a watchable ad (Mobile only) or a Booster (Steam only) for an additional +100% multiplier.

XP Table
At end of match, a set amount of Tower XP is earned throughout all towers. It is a pool of Tower XP that is split based on the percentage of money spent on each tower type. The losing player recieves 50% of the xp the winning player gets. However, the percentage increases as rounds go later. Note that the XP Table does not include the amount of XP heroes gain.

(Editor note: Because the amount of XP fluctuates based on what round you end in, I believe that the amount of time taken in a battle influences the amount of XP one gains. Yet to be confirmed.)

For reference:


 * Base: Red Bloon Camp / Yellow Stadium
 * +5%: White Wasteland
 * +8%: Lead Dungeon
 * +10%: Ceramic Crucible
 * +15%: MOAB Pit and above

*If no towers were placed and the opponent resigns immediately, you recieve 0 xp.

Summary
Pick a working strategy and stick with it for your games, which should give the best results for specialization, or vary strategies all the time to more evenly earn XP. Sometimes, selecting only as few tower types as is necessary will be better than going for all three types, not just because showing all tower types right away gives away your loadout to the opponent but this selectively chooses towers to apply XP towards. And most importantly, Hero XP (referred as "Hero Points" in-game) is completely separate from Tower XP, and therefore cannot "steal" Tower XP, so using a hero is still key.

It is also possible to surrender early to gain XP quicker, but it is often considered rude and unfair unless if you are playing against yourself or another person who doesn't mind surrendering. See information below for more details.

Tips

 * Buying and reselling the same tower counts towards the final XP ratio.
 * Try to only use the tower you want to upgrade, as this guarentees all exp goes to the tower.
 * Hero XP is seperate from Tower XP, so use them to increase your chances of winning.
 * Watch ads when win, as 30 seconds to get rewards is always worth it compared to an 8 minute battle for rewards equal to a win.
 * This option is only available in the Mobile version, however, but fortunately this game is cross-compatible with the Steam version.
 * Since ads (usually) aren't in PC games, Battles 2 on PC instead has XP tokens, which also applies a +1x modifier to XP similar to ads but there is no ad to watch.
 * Try to spend as much money on the tower type you want to get the most XP from, as this makes sure that more XP is put into the tower you want to get XP for.
 * Anti-stalling rounds helps accumulate Tower XP sooner. However, pairing Banana Farms to gain income sooner is pointless as the opponent (or you if you have two working devices) could just surrrender which has the same effect of losing all lives, but it cost 0 cash to surrender and is without the detriment of a tower stealing XP.
 * If one has two devices that can reliably play Battles 2, then that person could play against themselves in private matches to guarantee XP on their main account. Make sure that the other device has a separate account to Battles 2 so that it doesn't prevent both devices from playing the game.
 * According to this comment by u/thewarrior71 on this Reddit Post, this is perfectly legal as long as you don't try to do this in Ranked or Casual Matches.
 * If you don't have two devices that can reliably play Battles 2, there is also the official Ninja Kiwi Discord in the Battles 2 Private Match server where people can request matches solely for XP grind, among other things.
 * Accoring to this Reddit post by u/FlareonLover, its most optimal to win/lose on round 6 as opposed to Round 11 due to gaining 80% the XP for about 2/3 the time to Round 11. This be can really useful in private matches against yourself or another person in.
 * It is possible for Banana Farm and Monkey Village to get 100% XP without using another tower type. This is done with using a Hero, (perferably Qunicy, as he is best suited for early game, which is where all rounds for optimal XP gain are located) which doesn't steal tower XP and placing down either a Monkey Village or Banana Farm. Monkey Village could also be used to buff that hero at the same time, making it easier to hold off the bloons while the Banana Farm could be used to purchase hero Levels sooner.

Trivia

 * The most expensive upgrade to have its XP refunded after Version 1.0.2 belongs to Radar Scanner, at 2500 XP. This was enough XP to unlock Primary Training immediately.
 * Due to the amount of XP required for Tier 5 upgrades that was discounted from the transition of 1.0.8 to 1.1.0, that for most towers, Tier 4 upgrades are technically free. This is because the sum for most Tier 4 + Tier 5 upgrades requirements in 1.1.0 are the same or even less than just the Tier 5 upgrades XP requirements in 1.0.8.