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COMMON BATTERY SIZES 187

amp- hour rating of the cell. For a 5- amp- hour battery, a safe recharge level might be 500 to
2500 milliamps.
Limiting current is extremely important when recharging NiCd and NiMH cells, which can
be permanently damaged if charged too quickly. Lead- acid batteries can take an occasional
“fast- charge.” However, repeated quick- charging will lessen the life of the battery.
The recharge period, the number of hours the battery is recharged, varies depending on
the type of cell. A recharge interval of 2 to 10 times the discharge rate is recommended.

Recharging Batteries

Nickel metal hydride, rechargeable alkalines, and rechargeable lithium- ion batteries all require
special rechargers. Avoid substituting the wrong charger for the battery type you are using, or
you run the risk of damaging the charger and/or the battery— and perhaps causing a fire.
Batteries are recharged by applying voltage and current to their power terminals. Exactly
how much voltage, and how much current, depends on the type of battery. Some general tips
and observations:

• Most lead- acid batteries can be recharged using a simple 200- to 1000- mA battery charger.
The charger can even be a DC adapter for a video game, as long as the output voltage of
the DC adapter is slightly higher than the voltage of the battery. Remove the battery from
the recharger after 24 hours.
• Standard NiCd batteries like to be recharged slowly, typically with currents under 100 or
200 mA. Use a charger that supplies too much current, and you will destroy the cell.
• Rechargeable alkaline, NiMH, and lithium- ion must use a battery charger designed for
them. High- capacity NiCd batteries can be charged at higher rates, and there are recharg-
ers designed especially for them.
• Always observe polarity when recharging batteries. Inserting the cells backward in the
recharger will destroy the batteries and possibly damage the recharger.
• Lithium- ion batteries can catch fire if they are incorrectly recharged. Only use a recharger
specifically designed for the cell or battery pack you are using.

Robot Batteries at a Glance

As you’ve seen, batteries can be rechargeable or nonrechargeable. And different battery types
also vary by the volts per cell. Table 18- 1 shows, in a nutshell, the common battery types most
often used in robotics, the nominal voltage they deliver per cell (when fully charged), and other
selection criteria.

Common Battery Sizes

Battery sizes have been standardized for decades (see Figure 18- 7), though most consumers
are familiar with just a few of the more common types: N, AAA, AA, C, A, and 9- volt. There
are many other “in- between” sizes as well.
For the most part, the size of the battery directly affects its capacity— assuming the same
types of batteries are compared. For example, because a C battery provides roughly double

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