I have mine filled 4 times a yr. Once a qtr . my abs rep calls me and I bring my tank to work and he fills it . airgas in basically in my parking lot so I could get it filled there in an emergency
The 3L has a holding time of 20 days. It is probably best used as a shipping container. Having to recharge every 20 days would be a pain not to mention expensive.
Select Sires charges me $30 Per quarter. My tank holds well but they are in my area every quarter so they top it off. I usually have 6 to 7 inches which is plenty.
Mine is a pretty big tank that we got at a farm sale. It is a 20 week tank so 4 + months. I also get it recharged every 3-4 months and runs about $40-$45. I drop it off at a dairy near me when he is due for a visit, or take it to the ABS guy about 10 miles away when I am going in that direction and leave it for a couple of days.