The CardiLink Battery is a replacement for your depleted battery within your monitoring module. You will have a monitoring module if your defibrillator is the St John Ambulance HEART One or HEART Two. St John Ambulance acts solely as a reseller of the CardiLink product and is not the manufacturer or provider of any associated service. Customers are advised to review CardiLink's Terms and Conditions before completing their purchase. By purchasing the CardiLink product, Customers acknowledge they have reviewed, and agreed CardiLink's Terms and Conditions, as amended from time to time.