Cells and Batteries, Logan Storehouse Radio Net., Cache Valley, Utah, 18 January 2015
Given by: Quentin Gardner, Jr. WQ7G

Subject: Cells and Batteries

This is a brief coverage of a few terms that are used with cells and batteries, that amateur radio
operators should be aware of. They write 300 page books on this subject, so this is a brief list.
In some cases, the terms are an over simplification of what is happening or meaning.
It is always best to follow the cell or battery's manufacture guide lines when working with their cells or batteries.
Cell: A cell converts chemical energy to electrical energy.
Cell Types: Wet Cell are filled with fluid type electrolyte.
Dry Cell has a wet paste in them that holds the electrolight.
Jell Cell is similar to a dry cell, but are more wet.
Battery: Batteries are made of two or more cells.
Battery Types: Primary Batteries or Cell, are single use; non-rechargeable.
Secondary Batteries or Cell, are rechargeable.
Energy Density: It is a measure of how much energy is in a given volume of Cell or Battery.
When compared with other cells, higher energy density means a smaller cell can
supply the same amount of power or the same sized cell can supply more power.
Self Discharge: This comes from chemical reactions that are happening inside the cell as
it sits and waits to be used.. It is more commonly known as self life.
A typical self discharge rate for primary type cells and batteries is between 8% to
20% per month. Secondary type batteries self discharge rates are even worse
then the Primary batteries.
Higher ambient temperatures increase the self discharge rate. Lower
temperatures slow the self discharge rate. But, freezing batteries are always
destructive to the battery; unless it has been designed for freezing temperatures.
Depth of Discharge: There are Normal Discharge Batteries and there are Deep Discharge (Cycle)
Batteries. These batteries are designed to be discharged to a much low voltage
then it would normally be for the battery type. Examples of deep discharge
batteries are batteries that are designed for use in: Marine, RV and Golf Carts.
Discharged Voltage: It is the voltage that the battery reaches, as defined by the manufacture, when it is
considered fully discharge.
For examples: Alkaline cells are 1.5 Volts charge, but they are considered fully
discharge when they reach a voltage of 0.9 volts. And for a lead acid cells
2.1 to 2.2 volts per cell for a full charge. A discharged cell voltage is 1.95 volts.
Capacity: Is a measure of how much energy can be withdrawn from the battery. It is usually
measured in an Amp Hour or milli Amp Hour. It's a measure of how much current it
can supply for one hour; reaching it's discharge voltage.
Internal Resistance: It is a measure of how much resistance that a battery has, internally, to the flow
of current. It is not a measure of wire or resistor type resistance that makes up
the battery, but the inability of the electrolyte to move the electrons in the
chemistry to the other electrode. It is more of a physical resistance to the moving
of the electrons in the chemistry and it acts like a resistor limiting the current
flow through the battery.
If it was not for Internal Resistance a 110 mAhr alkaline button battery could
supply 56.32 Amps for 2.97 seconds. That would be nice. But, if you try it, you
will probably be disappointed. This is were super capacitors take over. They can.
Charging: Some batteries require charging by constant voltage and other need to have a constant
current supplied for charging. And still others need to have the charging take place in
steps; these are mostly the new hi-bred batteries.
Cell Balancing: Some types of chargers for the newer hi-bred batters will discharge and then
charge the individual cells in the battery and instead charging them as a group.
This is usually referred to as cell balancing.
So, it becoming extremely important to use the correct type of charger or method
for your batteries.
Rapid Charging: Rapid Charging is a means of charging a battery faster then normal. It will
shorten the battery's life and produce higher out gassing during the process. Not
to mention the thermal heating of the battery will be much grater, even to the
point of being dangerous.
It should only be done when the manufacture has made provisions for it; with a
special charger. Even then, it will still shorten the battery's life by quite a bit.
Out Gassing: Out gassing is when the cell produces a gas byproduct, that needs to be vented.
Out gassing is mostly associated with charging. But! Can also occur while discharging.
I have personally seen a lead Acid battery explode, when the hydrogen gas it produced
was ignited from a spark, as wires were being connecting to it.
I also have experienced an alkaline “AAA” cell pop open in a pager that I had in my
pocked. It blew the battery door off the pager. It did this, because the cell's vent was
defective and did not vent the gas it produced during discharge.
Memory: A battery Memory happens when the battery is consistently partially discharged. And
over time it will build a memory at that point. Then when you use the battery past that
point it will not be able to supply it's normal power and will become dead; even if you
have not used all the energy in the battery.
This effect can be prevented simply by fully discharging, to the minimum discharge
voltage as recommended by the manufacture, and then fully charging it again on a
regular basis.
This applies mostly to Nickel Cadmium type batteries and not so much to to other types.
Nickel Metal Hydride cells (NiMH) cells, although similar in chemistry, suffer less from
memory effect.
Trickle Charging: Trickle charging is a type of charging that is not meant to charge the battery after
a discharge, but to maintain a full charge while weighting to be used. It replaces
the energy that is lost do to self discharge of the battery.
The lead Acid battery needs to have a trickle charge, to keep them healthy and
ready. If not fully charged, a lead acid battery can build up lead sulfate on the
plates, which causes them to lose their ability to lose and attract electrons during
discharge. Preventing them from supplying the power when needed.
Lead Acid Batteries: The Lead Acid Battery are the most common battery that amateur radio operators
use in field. It comes in hundreds of types and thousands of sizes and styles.
They will last a long time, if taken care of properly. They are simple to take care
of. They just need a little attention.
The self discharge rate for lead acid batteries is approximately 1% per day at
77°F (25° C). Faster for higher temperatures and slower for lower temperatures.
See the manufacture's instructions for the best steps to take for the type and style
of battery that you have.
As a general rule:
1) Keep it charged. This helps to prevent lead sulfide of the plates.
2) Check the electrolight level, when charged.
3) Check the specific gravity of the electrolight in each cell, with a battery
hydrometer, when it is fully charged. This is the best way to check the health and
charge in a lead acid battery. *
4) Use a trickle charger that is made for lead acid batteries and of the correct size,
to maintain the charge while not in use.
5) Keep it clean. If dirt gets into the cell's electrolight, it weakens the sulfuric
acid in the electrolight.0
6) Use steam distilled water when adjusting the electrolight level. There is
minerals in tap water and the sulfuric acid in the electrolight will dissolved them
and be weakened by doing so.
More info: The battery manufacture is always the best source of information for the battery
that you have.
But, for general information you can use some of these sources.
The ARRL books: “Radios to Go! Getting the Most from Your Handheld
Transceiver” and “The ARRL Handbook for Radio Communications”
Wikipedia is another source for general information. Try looking up:
Battery nomenclature, Comparison of battery types, Battery balancer
Trickle charging, Rechargeable battery, Automotive battery, batteries
List of battery types, List of energy densities, and etc.
Non-Wikipedia Reference:
Introduction to Deep Cycle Batteries in RE Systems
http://www.windsun.com/Batteries/Battery_FAQ.htm#Battery%20Voltages
http://www.buchanan1.net/lead_acid.shtml
* A side note about specific gravity:
A lead Acid battery is fully charged that has a specific gravity of 1.265 @ 77° F (25° C)
(battery temperature). For temperature adjustments, add 0.004 to the specific gravity for
every 9° F (5° C) above 77° F (25° C) and subtract 0.004 for every 9° F (5° C) below
77° F (25° C).
As a general guide line: If specific gravity is approximately 1.265 @ 77° F (25° C), the
cell is charged and in good condition.
Specific Percent of
Gravity Charge
1.265 or higher = 100%
1.239 = 75%
1.200 = 50%
1.170 = 25%
1.110 and lower = Fully discharged.
If there is 0.03 difference between any two cells, it is an indication that there may be a
problem with the battery.
If the charger indicates a full charge and the specific gravity is lower then 1.265 in a cell,
there is a problem with that cell. Usually it's only one cell that goes bad in a lead acid
battery.
Specific gravity has a significant effect on the freezing temperature of a lead acid
battery.
If a lead acid battery freezes, it can split open.
Percent Specific Lead Acid Battery
of Charge Gravity Freezing point
100 1.265 -75°F (-59°C)
76 1.225 -35°F (-37°C)
74 1.200 -17°F (-22°C)
50 1.150 5°F (-15°C)
0 1.100 18°F (-7°C)
<0 1.050 27°F (-2°C)