Re: Battery Life

Your question deserves more than a mindless response. First we need to
cover a couple of terms. The first is mAh (milli-amp hours) which is a
measure of battery capacity. To understand this term, an analogy can be
made between gallons of fuel in a gas tank and battery capacity. A 20
gallon gas tank has twice as much fuel capacity as a 10 gallon, and
similarily, a 1000 mAh battery has twice the electrical fuel as a 500
mAh battery.

Voltage is a measure of pressure or force that pushes electricity
through a wire. A NiCd used in a R/C radio has a typical voltage of
1.2. When fully charged, it may read somewhat more. Around 1 V is where
the voltage has dropped to a point where the radio system will no
longer function or what is commonly called a dead battery.

We want to know how much capacity the battery has down to the the point
we call a dead battery. To do this, we need to recycle it. A typical
recycler (Hobbico makes a couple) will discharge down to 1.05 Vs. To
find out the voltage at which it is dangerous to operate your radio
multipy the number of cells times 1.05: RX - 4.2 Vs, TX 8.4 Vs.

As the battery is discharged, it is losing electrical energy or
capacity. The recycler will read the amount of lost energy in mAh. A
typical R/C system uses electrical fuel at the rate of 250 mAh, so if
your readout at the point the battery is fully discharged is 500 mAh,
then it will theoretically operate your TX & RX for 2 hours. Note that
you must always discharge a fully charged battery for this reading to
have any sense.

Besides finding battery capacity, the main purpose of a recycler is to
determine the condition of your batteries. The rule is that discharged
capacity should equal 70% of the rated capacity. For example, if the
battery's rated capacity is 1000 mAh and it's discharged from a fully
charged condition, the mAh reading should be at least 70% or 700 mAh.

NiCds do develop memory and as a consequence they lose capacity. The
only way to determine the health of them is to recycle. If the capacity
has dropped to a dangerous point, recycling can salvage the battery,
but you should expect to have to run it through several cycles.

I have switched to NiMhs simply because thay have greater capacity than
NiCds (two to three times as much), and they don't develop memory.
However, they won't provide the current flow (amperage) that NiCds
will. Also when left unused, they discharge at a higher rate. Finally,
if you store your batteries, always discharge them.


Ciao,

Mr Akimoto

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