Biomedical Engineering Reference
In-Depth Information
FIGURE 2-11
Energy density
comparison of
primary and
secondary batteries.
[Adapted from
(Buchmann 2005).]
FIGURE 2-12
Energy comparison
under load.
[Adapted from
(Buchmann 2005).]
It can be seen that although the alkaline battery is good for low discharge rates its
performance in this case is poor. It can also be seen that the performance of the Li-Ion
secondary battery is approaching that of the primary lithium type. A comparison of the
energy densities of a number of rechargeable batteries is shown in Figure 2-13.
Rechargeable batteries have a very low internal resistance. This allows high current to
be drawn on demand, which is essential for many digital devices, and to drive switch-mode
power supplies, which have high
inrush
currents.
Their main disadvantages include a limited shelf life and high self-discharge. Whereas
a primary battery may have a shelf life of 10 years, lithium-based batteries are good for
2-3 years in normal use, though cool storage at moderate charge prolongs longevity.
Nickel-based batteries have a shelf life of up to 5 years but require careful priming to
regain performance after long storage.
FIGURE 2-13
Rechargeable
battery energy
density.
