From the instructions:
"Do NOT use if:
• You have an electronic implant (e.g. cardiac pacemaker).
• If you are in the early stages of pregnancy.
• If you are being treated for existing DVT (deep vein thrombosis).
• If you have broken skin on the soles of your feet.
Please get your doctor's permission before using theBodi-Tek Circulation Plus Active if:
• You have a history of heart disease or cardiac condition.
• If you suffer from epilepsy or multiple sclerosis.• If you suffer from diabetes.
• If you suffer from phlebitis in its active phase (inflammation of a vein).
• If you suffer from inflamed tissue through disease or injury.
• If you suffer from varicose veins in its later stage.• If using for a medical condition.
• If you suffer from reduced sensitivity in lower legs and feet (associated with diabetes).
• This appliance is not intended for use by persons with reduced physical, sensory or mental capabilities, or lack of experience and knowledge, unless they have been given supervision or instruction concerning use of the appliance by a person responsible for their safety.
• If you are in any doubt about using the Bodi-Tek Circulation Plus Active for any reason, please consult your doctor before use."
https://www.manualslib.com/manual/1256465/Bodi-Tek-Circulation-Plus-Active.html
There's no charging necessary for the device, as it's mains-powered via a 9-volt adapter. It's supplied with one 85ml tube of conductive gel. (A small amount has to be rubbed into the soles of the user's feet before using the machine). Additional tubes of conductive gel can be purchased online:
https://www.bodi-tek.co.uk/conductive-gel-85ml-6-tubes-for-price-of-5.html