Selection of a rechargeable internal back-up battery for a totally implantable artificial heart

Three kinds of rechargeable batteries, NiCd, NiMH, and Li+, were compared f or the purpose of selecting the most appropriate battery for use in a Recha rgeable Internal Back-up Battery (RIBB) unit for a Totally Implantable Arti ficial Heart. Batteries of each kind were connected in series to obtain the required driving voltage of 24 V. The NiCd and NiMH batteries were charged by a constant current of 1 C, and the Li+ batteries were charged first by a constant current of 1 C and later by a constant voltage of 28.7 V. All th ree types of batteries were discharged using a dummy electronic pulsatile l oad consuming 20 W of power. The tests showed that the Li+ batteries were c apable of supplying the required energy for more than 60 minutes. The Li+ b atteries had a specific energy of 121.5 Wh/kg, which was more than 3x that of the NiCd and NiMH, and an energy density of 282.5 Wh/L more than double that of the other two. In addition, the Li+ batteries recorded the least te mperature rise during charging and discharging. The results of our tests co nclusively showed that the Li+ battery is the best among the three for use in an RIBB from the viewpoint of energy density and temperature rise.