We have sold this product for over 30 years, and since 1977 it has been one of our most popular items. Over the years, the manufacturer has made changes to this system, and each time, the product was given a new part number. So if you already own this system, it may be referred to as an AH1, AGH1, AH5, AH15, or AS200. The original systems were manufactured by Racal Health & Safety. Many years ago 3M purchased that company, and the Airstream line became a 3M product. The original AGH1 and the newest of the AS400's are all compatible. Batteries, chargers, filters, and all replacement parts are interchangeable and compatible. The filters for the new AS400 will also fit the original AGH1.