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.