I have read the battery sticky and read through the battery university. I understand leaving unprotected cells on a charger overnight is a bad idea. The problem is the cheap chargers available on most vaping sites don't stop charging, it's up to us to keep a eye on them and remove the cells once the indicator lights change to the charged color. From what I have read the most dangerous time is when charging cells especially if they are under voltage. Now I have protected and unprotected cells. The protected cells just barely fit into my trustfire charger. I have unprotected cells for a pack and have a protection ckt. built into that particular device. I'm hoping there are smart chargers available that sense voltage and stop charging at 4.1 volts or a voltage deemed same. I have searched and googled but always came up with cheap chargers without a true stop charging or smart system. I mostly use 18650 batteries from 2000 to 5000 MAH. I appreciate any information, I just want to be as safe as possible charging some of these high MAH cells.