I just got a passport, but I found my charger output is only 5V - 850mah. It is pretty slow charging (almost 4hrs).
I changed to use my Nexus 7 charger (output 5V-2A), but it is not much better (around 3h30m).
May I know your passport with original Charger take how much time for charging? And maybe the original charger will make the battery usage time better/ per charging?
It may depend on your region, but our Passports came with larger chargers than the 850ma. I don't have one in front of me, but I think they are 1300ma.
If you are using a charger not made by BlackBerry, it may not be wired to signal it is a higher output charger and the phone will only draw about 500ma from it.
The Playbook chargers are probably the best and can be found cheap.