This is to answer the question of why the rapid charging adapter states an output current of 2A while the product says it has a charging current of 4A.
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These are two different definitions regarding the charging speed
Check the images in the product page https://www.nitecorestore.com/Nitecore-NBP68HD-Rechargeable-Battery-Pack-p/bat-nite-nbp68hd.htm
1) 4A charging port on the battery pack
2) 2A adapter (what you see on the adapter specification)
2A is the maximum output current from the adapter while 4A is the maximum charging current applied by the charging circuit in the NBP68HD battery pack. The only correlation between the two is that the maximum output power (2A x12V) from the adapter must be larger than the maximum charging power of the battery pack (4.5V x 4A). In this case, a 2A adapter is able to provide enough power to charge the battery pack at maximum of 4A. (The actual charging current is a variable between 0-4A depending on how full the battery is.)