I charged my light overnight and it's not full, why?

Since we made a non-proprietary charging system (USB) it means you can use any USB charger with the lights. The problem is that all USB chargers are different and there are a TON of different power protocols and negotiation methods, so for example, if you plug your Evo (10Ah battery internally) into a 0.5A charger (like a the tiny white cube that comes with iPhones) then it will take 10 / 0.5 = 20 hours minimum to charge the light. By contrast, if you plug it into a 5V/3A or a QC3.0 charger it will charge at 6x the speed of the 0.5A charger and thus only take ~4 hours total including trickle charging.

What's trickle charging? This is an inherent property of Li-Ion batteries that every single charging system has to deal with, where the amount of charge you can push into a battery tapers off as it approaches fully charged. As an example, if your light is completely dead, it will charge at 3-amps from a 3A charger, but as it gets above ~85% full it will drop the charge current significantly until it reaches 0-amps when full, so generally speaking the first 85% of the battery charges way faster than the last 15%, thus the "trickle charging" that occurs when close to full.