In Star Wars: Galaxy of Heroes, when you level-up a character, you can use any number of training droids (from 1 to however many you have) just to gain 1 level. Why use several? Does it give you better chance at high bonuses? If so, at what point does using more give no more advantage?
You can gain more than one level at once by using multiple drones, it just doesn't look like you do because the little level up meter animation doesn't appear to go more than one. However you can see that the level number will still be higher.
Another possible explanation might be that you've reached your characters' level limit.
There is no advantage to using more or fewer drones at once. It costs the same credits per drone whether you use 2 or 50 and you get the same amount of stat gain.
Exp given and cost per training droid:
- Tier 1: 30XP, 213 Credits
- Tier 2: 150XP, 1065 Credits (5x Previous Tier)
- Tier 3: 750XP, 5325 Credits (5x Previous Tier)
- Tier 4: 1500XP, 10,650 Credits (2x Previous Tier)
- Tier 5: 3000XP, 21,300 Credits (2x Previous Tier)
- Tier 6: 6000XP, 42,600 Credits (2x Previous Tier)
- Tier 7: 12000XP, 85,200 Credits (2x Previous Tier)
The cost per XP point remains the same for every tier of training droid (7.1 credits per XP).
Characters need increasing amounts of XP as they level up, so more droids are required at each level.
The only time choice of droid matters is when you are leveling a character to max level, as any XP over the max is lost. So if you use (for example), 5 5* Droids when 4 5* and 1 1* Droid would have also given enough XP, you are wasting credits to level up.