I'm looking at ordering a Vaporesso Polar and one of the concerns I've read is the heat generated from charging at 2.5A. I'm just curious about that... Does it really heat up that much? Is it safe? Is it harder on the batteries? I'd prefer not to have to buy a separate charger and I'd sooner buy a mod with slower charging rather than destroying batteries.
I use the Polar and charge it on board. It charges really well and I haven't experienced the mod heating. In fact, I only ever charge it onboard because my external charger is slow (1A or 1.5A I think). At 2A or 2.5A on the polar, the charge time is reduced significantly and the mod even gives you an estimation of when it'll be 100% charged. The estimations are per battery.
As a test, I put 2 batteries which aren't paired and have different battery life to see how the mod will go about charging it and it seems that the mod charges each battery individually because on the screen I was able to see the percentages for each battery as well as an estimate of how long it will take.
The polar is in my opinion a really nice device. I love the fast charging feature and how fast the mod fires up.
With that being said, I do recommend getting an external charger at some point. Although charging onboard with this device was pretty safe for me, its hard to garauntee the same for everyone and a charger is nice to have in case the batteries are unbalanced.