Right now, the Samsung 25R is just about the most popular battery in the vaping world. It's the only battery I use and I keep 4 in constant rotation.
The NiteCore D2 or D4 is a top notch charger.
You can find both of these items on Amazon, but look for fulfillment by Amazon and not a 3rd party vendor. I'm a prime member and purchased my charger through Amazon, but not the batteries.