Interferential therapy has been around since 1951, originating in Germany, as a method to ease the pain the chronic pain patient suffered. The patient would come in to the Doctor's office or hospital for a treatment from the interferential machine and stop the pain during the treatment and for an extended period of time following the treatment, referred to as carryover pain relief.
The reason for the inhouse treatment was the equipment was very expensive and it needed a large supply of electricity to work. The interferential machine actually goes off and on over 8,000 times per second as compared to the traditional TENS unit ( transcutaneous electronic nerve stimulator) which does so only 150 times per second. This demand for electrical energy exceeded the ability of electrical engineers working with portable battery systems to develop any form of battery which could meet the excessively high demands of a clinical interferential machine. Literally throughout the history of interferential therapy the problem in making the units available for self treatments has revolved around the high demand for electrical energy and the ability to have that capacity yet still be a small, portable device.
A simple analogy is if one were asked to fill a 10 gallon tank with a one gallon bottle of water and the person could not go back to refill the bottle. Obviously it can't be done and the time period to try would be 1/10th since the bottle would be exhausted of all water after one discharge. Battery systems also have a "limited capacity" of electrical energy and interferential exhausts most of that capacity very rapidly. Typically when anyone tried to manufacture a truly "portable interferential device" and used a 9 volt, triple A, or AA disposable or rechargeable battery system, the batteries had no charge left in less than 5 minutes. To create more capacity meant the batteries would require a wheelbarrow to transport them in which means portability is lost.
Practically speaking there is no economical way to overcome the battery problems, yet maintain portability, other than by engineering a unit with an AC adaptor. Once you have an AC adaptor then the entire grid that supplies electricity is now available. Most people have access to some form of wall outlet so a unit can be plugged in to the outlet and treatment can begin. By using an AC adaptor pain patients no longer have to go to clinics or hospitals for treatments and can self treat with lasting carryover pain relief.
The Infrex Plus on interferential mode using rechargeable batteries has an extended life of approximately 80 minutes before the batteries are fully discharged. This was accomplished by energy saving engineering and wave form adjustment coupled with pre-modulation inside the unit. Clinical interferential treatments are generally for 20 minute duration so the 80 minutes provides true patient comfort using only the battery system when necessary. Standard treatment practice should be to use the AC adaptor at all times and only use battery system when can not access outlet.
The video on How To Use An Infrex Unit shows how the portable unit operates including using it with a rechargeable battery system.