Looking for Amp rating to charge camper Vacuum

I recently picked up a used Bissell Lift-Off Floors and More stick vacuum, model 75Q3-T from a church garage sale. Unfortunalty it did not come with the charging brick. Now usually one can look on the unit and it says what the input volt and amp should be. This one only reads 12 volt.So, I am worried that if I use too large of an amp.mA on the thing I will fry its innards.
Short of calling Bissell and ordering a $20 charger, does anyone have any idea on what the amp rating of the charger should be?