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Battery Information: 
Battery Info.
Content links:
Electrolyte  ELECTROLYTE
VRLA (valve regulated lead acid) Battery  VRLA BATTERY
Gel Cell Battery  GEL CELL BATTERY
AGM (absorbed glass mat) Battery  AGM Battery
Flooded Type Deep Cycle Battery  FLOODED TYPE BATTERY
Self-Discharge Rate  SELF-DISCHARGE RATE
Charge Rate  CHARGE RATE
Electrolyte Level  ELECTROLYTE LEVEL
Equalization Charging  EQUALIZATION CHARGING
State of Charge  STATE OF CHARGE
Battery Location  BATTERY LOCATION
Used Batteries  USED BATTERIES
Battery Safety Battery Safety
Sizing Your Battery Bank - having the proper size battery or battery
bank can mean the difference between success or disappointment in
an alternative energy or stand-by power system.
First off, I do not think it is possible to oversize a battery system. The larger
the battery bank, the less work it has to do and the longer it will last.
Many people undersize their battery bank thinking that just because the
batteries are deep-cycle you can work them to the bone and they will
continue to take it.
In an undersize battery system the batteries are continually depleted into a
deep state of discharge and then  forced to play catch up.
These wide swings of battery state of charge shorten the battery life in
addition to doing something that most people don't consider.
If the battery system is not matched to the loads and it is drawn down too
low - time to fire up the generator. The money you spent on your photovolatic,
wind or hydro system will be sitting idle while you get to enjoy the sounds
and smells of a generator.
DEEP CYCLE BATTERY - these batteries are made to be discharged
(run down) to a very low percentage rate of full charge. Their plates are thicker
than automotive SLA (starter,lighting,accessories) types. They will not work
well to start an engine as they are not designed to produce a lot of power
(amperage) over a short period of time. This is where a regular automotive
battery shines. By the same token, an automotive starter battery is designed
to put out a lot of amps for a short period of time but not to have a large
percentage of its capacity used. When an automotive battery is heavily
discharged or left in a low state of charge (less that 60% of capacity) it is
time to call a tow truck. In a stand-by or alternative energy environment this will
not work. Deep cycle batteries are designed to be cycled to a relatively low
state of charge (in many cases, 20% of capacity.) Their storage capacity is
measured in amp hours with a given discharge time (usually a 20 hour rate
 {sometimes a 100 hr. rate}.) In theory a 100 amp hour battery will produce five
amps (five amp hours) for twenty hours before it is exhausted. Automotive
batteries are rated in cold cranking amps which are meaningless for back-up
or alternative energy purposes.

ELECTROLYTE - the liquid in a storage battery which is composed of acid
and water. NOTE - a battery (of any kind) does not store electricity, very few
things will. A storage battery converts elecitricity coming in and stores it in the
form of chemical energy. When power is pulled from the battery it converts the
chemical energy back into electrical energy. There are always some losses in
these conversions.

AGM batteries are considered sealed batteries.
Water can not be added to them.
If any electrolyte is lost, it is lost for good.
The plugs on the top or sides of these batteries are pressure relief valves.
If, by overcharging one of these batteries, the pressure will vent (and possibly
some electrolyte), it will be released through these valves.
This is done to keep the battery case from bursting when improperly used.
As these batteries operate at higher internal pressure than the surrounding
air, oxygen and hydrogen gasses produced during charging (greater than 99%
as a rule) are recombined internally back into water for the electrolyte.
VRLA type batteries do not accept high amperage/voltage rates of recharging
as well as a conventional flooded battery.

GEL CELL BATTERY - the electrolyte is mixed with a silica material which
converts it into a gelatin.
This keeps the water and acid mixed and allows the battery to be used in
any position as there is no liquid to run out.
These are the safest for use indoors.
They are the least affected by temperature extremes (especially freezing.)
Their tolerance for being stored at a low state of charge levels is excellent.
They do not tolerate overcharging well but as a rule can handle a higher
charging voltage than an AGM battery.
Cost is approx. $ 2.00 per amp hour.


AGM (ABSORBED GLASS MAT) BATTERY- the liquid electrolyte has been
absorbed into a fiberglass cloth mat between the plates.
These have good deep cycle characteristics and can be used in all positions.
They are less affected by temperature extremes than a flooded type battery
but are more sensitive than a gel cell battery.
AGM batteries do not tolerate storage at a low state of charge as well as a
gel cell.
This type of battery does not handle overcharging - especially at a high
charging voltage.
Can be used indoors. Cost is approx. $ 1.50 per amp hour.

FLOODED TYPE DEEP CYCLE BATTERY - similar to the kind used in
automobiles in that the electrolyte is in a liquid form. Excellent deep cycle
characteristics. Must be vented outdoors to dissipate the hydrogen gas which
is produced during charging. Can not tolerate temperature extremes as well
as Gel cell or AGM batteries. Should not be left in a low charge state as
permanent damage could result. These are the best deal for large storage
needs. Cost is approx. $ 0.50 per amp hour.

SELF-DISCHARGE RATE - a fully charged battery will lose from one to four
percent of its charge per day when stored without being connected to a
charging system (maintenance type) @ 75 deg.F. The higher the temperature,
the higher the rate of self-discharge. Gel cell and AGM batteries have a very
low rate of self-discharge.

CHARGE RATE - a good charge rate is approximately 10% of the total
capacity (of the battery or battery bank) per hour (i.e.- 200 amp hour battery
charged at 20 amps.) This is called C-10 and will  reduce electrolyte loss and
damage to the plates. NEVER attempt to charge a battery that is frozen, it
can get ugly.

ELECTROLYTE LEVEL - flooded type batteries should have their levels
checked monthly (more often if under heavy usage.) Do not overfill, as the
liquid will expand (due to gas bubbles and a rise in temperature) when it is
being charged. Electrolyte levels should never be allowed to fall below the
top of the plates. When resting in a low discharge state for a long period of
time the electrolyte can crystalize  in the plates and permanently damage them.

We use a jug type of battery filler. It will only dispense
water when the nozzle is pressed into the cell opening and will shut off
automatically when the level reaches the nozzle. These are available from
auto parts houses such as J.C. Whitney and others for less than ten dollars.
As long as you always make sure that the gasket is in the groove after refilling,
these last for years.

EQUALIZATION CHARGING - flooded type batteries should have an
equalization charge (controlled over-charging) done periodically. This
keeps the acid mixed throughout, loosens and removes some of the
sulfates that form on the surface of the battery plates (reducing capacity)
and can help if the battery has a weak cell. When equalizing a battery it
is a good idea to cover the caps with a paper towel, wet spots (spitting)
can indicate a weak or bad cell. Before doing an equalization charge,
make sure that the battery is at or near a full charge. This will reduce
heating which may occur when rapidly bringing a battery up from a low
charge state to an equalized state. NEVER top off the liquid level before
an equalization charge (make sure it covers the plates) as it can run out
of the cells when it expands and outgasses. It is a good idea to loosen
the battery caps prior to an equalization charge due to the high pressures
which can be created in the cells.

STATE OF CHARGE (S.O.C.)  - this is a measurement of how much
useable power is left in a battery or battery bank. This can be determined
by one of three ways.
The first two methods are accurate only if done when the battery has been
at rest for several hours. As a battery is being charged or discharged the
chemistry and physical characteristics of the elecrolyte change. Gas bubbles
are produced and the temperature as well as the acid to water ratio changes.
These changes can greatly affect the readings using the first two methods.
1st. - voltage measurement, on a battery at rest this method can show state
of charge by comparing the voltage to a chart showing the percentage of
charge relative to voltage. A freshly charged battery can show a higher,
inaccurate voltage, than one at rest. A recently discharged battery can show
a lower voltage than one at rest.
2nd. - electrolyte density measurement, a sample of the electrolyte is drawn
into a hydrometer which shows the density of the liquid. The heavier the
electrolyte (higher gravity), the more acid in solution, the higher the state of
charge. A freshly charged battery will have gas bubbles in the electrolyte
which can show a lower gravity and indicate a lower S.O.C. than actually
exists. A recently used battery can show an inaccurate S.O.C. due to acid
absorption in the battery plates which will disperse into the electrolyte upon
Both methods are effective when checking for a weak cell in a flooded
battery with filler caps which allow access to the electrolyte.
3rd. - amp hour metering, this method uses an amp hour meter which is set
 using the specifications of a new battery or battery bank at full charge. It
measures and records power (amps) going into and coming out of  the
battery and keeps an electronic balance sheet. You can see why this would
not work well on a used battery system as there would be no accurate
starting point. These meter systems run from a few hundred to several
hundred dollars.
IN SUMMARY: the most important thing is to properly maintain your battery
or battery bank and learn its characteristics.

BATTERY LIFE - depends more on the user than any other factor. Do not
allow the battery to become overheated as this will dramatically shorten its
lifespan. A battery has a lower freezing temperature when it is fully charged.
Keep the electrolyte levels where they belong and make sure that all posts,
cables and connections are clean and tight. It is a good idea to coat
exposed metal posts and connections with a battery preservative.
Manufacturers rate battery life by the number of charge/dis-charge cycles.
The more times a battery is discharged to a very deep state, the shorter the
life span will be. As a rule, a larger battery bank will last longer than a smaller
one when both have the same input and output. The larger bank will
discharge to a higher percentage of capacity than the smaller one.
A little maintenance goes a long way to protecting your investment.    

BATTERY LOCATION - as we have said, don't let your batteries get too
hot or too cold, and please vent them to the outdoors. Vapors coming
off of flooded batteries can be very corrosive, especially when the battery is
undergoing an equalization charge. When being charged, a flooded battery
produces hydrogen gas which is explosive.
Just as important is accessibility.
If you can't get to your batteries, can't easily see the electrolyte levels or
can't easily top off the electrolyte, YOU WON'T. The first battery bank we
had consisted of eight, 6 volt - 220 amp hour golf cart batteries, two to a
shelf. The shelves were so close together that I had to use my finger
(real smart) or a mirror to check the electrolyte levels along with a bulb
type water dispenser to top them off (as well as to run them over.) After
the first set of batteries died prematurely, I figured out what was wrong.
Now we can check and water our battery bank in minutes and without any
difficulties. Human nature, being what it is; if it is a pain in the neck to do,
you will not do it.
If you locate your batteries outdoors it is recommended that you try to
keep the battery enclosure out of direct sunlight as battery life is greatly
shortened by high temperatures. Keep an airspace between
each battery to keep them from over heating. In cold climates, insulate
the enclosure as when the batteries are subjected to low temperatures
the chemical reactions which take place in them slows down.
Lead acid batteries work best and last longest when kept at 75 degrees
Keep your battery tops clean and we coat all exposed metal parts of the
battery terminals and lugs with a coating of sealer made for batteries.
This greasy product works great - but do not get any of it on your clothes
as it will stain them permantly. On system rehabilitation jobs I gave up on
wearing anything but old clothes because of this.  

USED BATTERIES - I am a big fan on reusing everything we can. I do,
however have serious reservations about used batteries. Unless you know
the history and how the batteries have been maintained, you could buying a
pig in a poke. With batteries of unknown history, you could set your self up for
some serious disappointments and wind up with a lot of lead that you have to
dispose of properly. In some of the systems I have either upgraded or
reworked the client will offer me the batteries to resell. I tell them that I will
take them and dispose of them properly (to be recycled.) I have done this
with batteries that were only a few months old. It is bad enough to let yourself
done, it would be even worse if I let you down.
A note on Nickel-Cadmium storage batteries: some
years ago it seemed like everyone was selling and
praising used Ni-Cad batteries. There were companies
that refurbished them. After a couple of years the
interest died out. The batteries (even used ones)
were very expensive and had poor reliability. They also
had different charging requirements than lead acid
batteries. If you run across any and consider buying
them,  please give it a lot of thought.



BE CAREFUL around battery terminals and posts. An improper
connection or misplaced wrench can produce a devastating arcing
short circuit. Storage batteries contain enough energy to cause metals
to become liquid and spray in all directions. We use a small palm
ratchet wrench (it is too short to reach from post to post) when
tightening battery terminals. Also, watch when handling cables as they
can short out a battery if carelessly handled. I didn't read this
somewhere, I have done it. Aside from the safety concerns, nothing
makes you look more like one of the Three Stooges  than shorting out
a battery bank when connecting the cables.
copyright by John Drake Services, Inc.

A note on battery terminals. If your battery(s) have wing nuts to hold the
lugs in place, we recommend that you replace them with regular nuts. You
will get a more secure connection. On installations where the lugs have to
be disconnected on a regular basis, and without tools, then the wing nuts
make sense.  

12 volt battery wiring layout

24 volt battery wiring layout

48 volt battery wiring layout
It is plus to minus and so on. This adds up the voltage of each battery.

Measuring Battery State of Charge.
Battery voltage will vary for the same state-of-charge depending on
whether the battery is being charged or discharged, and what the current
flow is in relation to the size of the battery. The chart below gives you an
idea of state-of-charge for various battery conditions in flooded cell lead
acid batteries. Voltage varies with temperature. While charging, a lower
temperature will increase battery voltage. Voltage is 0.9 volts higher on a
12 volt battery at 32 deg. F than at 70 deg.F. While discharging, a higher
temperature will increase battery voltage. There is little temperature effect
while the battery is standing at rest.
This information is courtesy of Ralph Heisy, Bogart Engineering and from
Applied Power.

                                                                                                  Battery Voltage
Battery Condition @ 77 deg. F.
                                                                                      12 Volt                   24 Volt
battery during equalization charge
       over 15
      over 30
battery near full charge while charging
  14.4 to 15.0
  28.8 to 30.0
battery near full discharge while charging
  12.3 to 13.2                           
  24.6 to 26.4                    
battery fully charged with light load
  12.4 to 12.7
  24.8 to 25.4
battery fully charged with heavy load
  11.5 to 12.5
  23.0 to 25.0
no charge or discharge for 6 hours - 100% charged
no charge or discharge for 6 hours -
80% charged
no charge or discharge for 6 hours -
60% charged
no charge or discharge for 6 hours -
40% charged
no charge or discharge for 6 hours -
20% charged
no charge or discharge for 6 hours -
fully discharged
battery near full discharge while discharging
  10.2 to 11.2
   20.4 to 22.4
A hydrometer (which measures specific gravity [the density of a solid or
liquid in relationship to pure water which has a specific gravity of 1.0])
is very accurate at measuring battery state-of-charge if you measure the
electrolyte near the plates. Unfortunately, you can only measure the
electrolyte at the top of the battery. When a battery is being charged or
discharged, a chemical reaction takes place at the border between the
lead plates and the electrolyte. During charging, the electrolyte changes
from water to sulfuric acid. The acid becomes stronger and the specific
gravity rises as the battery charges. It takes several hours for the electrolyte
to mix and the gas bubbles to break out of the liquid so that you can get
an accurate reading at the top of the battery.
Always try to take readings after a long period of no charge or discharge.  

The chart below gives state-of-charge vs. specific gravity of the electrolyte.
These readings are correct at 75 deg. F.
 state of charge      specific gravity
100% charged           1.265
 75% charged            1.239
 50% charged            1.2
 25% charged            1.17
 fully discharged        1.11          
Please remember to use the thermometer inside of the hydrometer to
correct for temperature. 75 deg. F is the base-line (standard) and any
reading above or below this temperature must be corrected for an
accurate reading.