An implantable device containing a plurality of batteries, the plurality of batteries comprising: at least one first non-rechargeable battery; and at least one second rechargeable battery, wherein the implantable device is comprised within a single housing; and wherein said second rechargeable battery has a first state where its charge level is above a first threshold and a second state where its charge level is at or below said first threshold, characterized in that: said implantable device is configured to deliver cardiac electrical shock for a first therapy and powered by said first non-rechargeable battery when said second rechargeable battery is in said first state and when said second rechargeable battery is in said second state, said first therapy being one of cardioversion therapy and defibrillation therapy; and said implantable device is configured to deliver a second therapy powered by said second rechargeable battery when said second rechargeable battery is in said first state, said second therapy being one of Cardiac Contractility Modulation therapy and cardiac pacing therapy; said implantable device is configured to use said rechargeable battery, when in said first state, for powering sensing for said first therapy and for powering sensing for said second therapy. at least one first non-rechargeable battery; and at least one second rechargeable battery, wherein the implantable device is comprised within a single housing; and wherein said second rechargeable battery has a first state where its charge level is above a first threshold and a second state where its charge level is at or below said first threshold, characterized in that: said implantable device is configured to deliver cardiac electrical shock for a first therapy and powered by said first non-rechargeable battery when said second rechargeable battery is in said first state and when said second rechargeable battery is in said second state, said first therapy being one of cardioversion therapy and defibrillation therapy; and said implantable device is configured to deliver a second therapy powered by said second rechargeable battery when said second rechargeable battery is in said first state, said second therapy being one of Cardiac Contractility Modulation therapy and cardiac pacing therapy; said implantable device is configured to use said rechargeable battery, when in said first state, for powering sensing for said first therapy and for powering sensing for said second therapy. said implantable device is configured to deliver cardiac electrical shock for a first therapy and powered by said first non-rechargeable battery when said second rechargeable battery is in said first state and when said second rechargeable battery is in said second state, said first therapy being one of cardioversion therapy and defibrillation therapy; and said implantable device is configured to deliver a second therapy powered by said second rechargeable battery when said second rechargeable battery is in said first state, said second therapy being one of Cardiac Contractility Modulation therapy and cardiac pacing therapy; said implantable device is configured to use said rechargeable battery, when in said first state, for powering sensing for said first therapy and for powering sensing for said second therapy.