I'd highly recommend you read up on batteries and especially pay attention to what C rating is and how it relates to different battery chemistries.
A huge misconception I've noticed is that many think that a 2500 mAh 18650 battery has the same discharge rating as a 4000 mAh 18650 battery of the very same chemistry. This simply is not the case. The true amerage rating is based off of 3 things primarily. It's chemistry make-up, it's C rating (which is determined from chemistry and construction) and it's capacity. What this really means is that 10C 2500 maH battery can have a continuous load of 25A safely and the 4000 mAh one will have a 40A conitinous load rating. You can't just go off of it's an 18650 of the same chemistry make-up because the discharge rates are different!
Best thing you can do is to educate yourself fully on the battery you're using. Take a look at battery university's website on C-rating, battery discharge methods and lithium-based batteries information. I'd post the links but I'm not allowed to just yet.