| Chemistry |
Strength |
Weakness |
| Alkaline |
Alkaline batteries are popular for small electronic devices and toys.
These batteries have a high energy density and they are usually quite
inexpensive when you guy ``store brands''. |
Alkaline batteries have high internal resistance. This means even
though they have a high energy-density, it is not possible to release
energy at a fast rate. Furthermore, alkaline batteries discharge at
a linear slope. This means the output voltage continues to drop
linearly as the battery discharges. This characteristics affect
the torque or motors severely. Most alkaline batteries are not
designed to be rechargeable, making the long-run rather expensive. |
| NiCd |
Nickel Cadium batteries represent the majority of rechargeable
batteries. The internal resistance of NiCd batteries is small, making
these batteries dangerously efficient at fast discharging.
NiCd batteries can be trickle charged, which means a recharger can
be inexpensively made. Being rechargeable, NiCd batteries are
economical in the long run. |
NiCd batteries have memory effect. This means when a battery is
recharged without first completely discharged, the capacity of the
battery will be limited. Furthermore, NiCd batteries have a
relatively low energy-density. This means it takes more
mass to store the same aount of energy compared to high
energy-density batteries. |
| NiMH |
Nickel Metal Hydride batteries share many advantages with NiCd
batteries. In addition, NiMH batteries have twice the energy-density
of NiCd batteries. For the same size and same mass, a NiMH battery
stores twice the amount of energy. NiMH batteries also have low
internal resistance and are rechargeable. NiMH batteries do not have
memory effect, which means they do not need to be empty before
being recharged. |
Unlike NiCd batteries, NiMH batteries cannot be trickle
charged. This is a minor issue because it is still easy to
correctly charge NiMH batteries with a constant current source and
a voltage monitor. |
| Li-ion |
Lithium-ion batteries are used in many high-end cordless
and rechargeable devices. The energy-density of Lithium-ion batteries
is higher than that of NiMH batteries. |
Although Li-ion batteries seem very suitable for robotics, they have
some limitations. Li-ion batteries are not designed for continuous
high drain rate. This is why cordless power tools do not use Li-ion
batteries. It is also quite difficult to charge Li-ion batteries
with home made circuits. Li-ion batteries require constant current
charging for the first stage, then constant voltage should take over
for the second stage. |
