Where did you purchase those batteries? The label lettering on the shrinkwrap is much larger and different from the pics that I have seen previously of this model. That's not to say yours are not authentic, but a lot of battery countereiting is going on in China, and since this battery is so sought after it will be one of the most targeted to fake. It's also possible Sony has recently changed their labels. Just a heads up.
2 Sony US18650VTC3 High Drain 30A Rechargeable Li on 18650 Battery 1600mAh New | eBay
US18650VTC3 1600mAh high power rechargeable battery, View US18650VTC3, US18650VTC3 Product Details from Shenzhen Victpower Technology Co., Ltd. on Alibaba.com
I only use AW IMR batteries, so I can't help you concerning the Sony's. I do own a Nitecore i4 and my daughter has a i2. Our chargers don't get warm while in the charging cycle. My guess is as long as it is just "warm" that you will be ok, but always practice routine safe battery charging habits.
Monitor batteries & charger during charging, never leave batteries to charge overnight or while not at home to monitor them, and remove batteries after they are fully charged. Good idea to use the charger on a non-flamable surface such as a stovetop. Check battery voltage both after removing from your mod and when coming off of the charger with a meter to ensure the voltages are within accepted ranges. Fully charged batteries should be 4.2 volts and between 3.4 - 3.5 volts out of the mod.