Inka, no one can make the decision for you. I know there are some here that will put zero trust and will always expect the unexpected. I, on the other hand, while I do understand that one can make a stupid mistake and be careless (i.e. putting a loose battery in their pocket with a set of keys or loose change), I do put a bit more trust in the people that design and manufacture these devices. Using my iSticks as an example, you don't remove the batteries to charge them. Rather you plug in a micro USB cable into the mod and it charges it. The circuitry inside the mod is designed to charge the battery, and when the battery is fully charged, it will stop charging. Much like plugging a charger into your cell phone. I have no fear of my cell phone blowing up if I leave it on the charger overnight while I sleep, and I also have no fear of plugging in my iStick overnight to recharge while I sleep. If the battery sits fully charged in the charger an hour or two past reaching fully charged, that's not going to be a big issue....since the charger will automatically shut off anyway.
I doubt even the most paranoid will sit there and stare at the charger while their batteries are recharging, patiently waiting for the exact moment that the battery is fully charged and then attempt to remove the batteries so they don't sit in the charger for even 5 seconds more than necessary. If you look at the specs and features of any well regarded charger, they will all indicate that the charger will automatically stop charging the battery as soon as it is fully charged.
There is a HUGE difference between RESPECTING the potential dangers of batteries, and FEARING them. If you are going live in fear that any moment your battery may explode in a cataclysmic fashion if you don't treat it like it is a bottle of nitroglycerin or an old, corroding stick of dynamite, then you might as well forgo using a battery and fashion a hand crank generator to power your mod.
