Most welding supplies or fire extinguisher houses that fill bottles have the equipment to fill one, although some might not have the proper scale to accurately weigh a small 10 oz. Generally, I don't have a clue. The amount of pressure a bottle has is directly related to the amount of liquid and the temperature of the outside, or ambient, air. A full bottle installed in a car during the heat of the summer, will register roughly 1200 to 1500psi. Take that same bottle during the cold in November, and you'll end up with 800psi if you're lucky.
Temperature plays that important role.
That's why if you take a bottle to be refilled at a shop that can't accurately weigh it, you end up with usually one of two problems. Either it's been severely underfilled, which then tends to have you running out sooner. Or, it's been overfilled, which if left in the hot sun somewhere, will leave you with a bottle that will blow the safety blowoff valve located in the side of the shutoff valve. In addition, it will scare the ever living daylights out of you, if you're close by when it blows. One more word of caution here.