Q What is a Battery & How it works?
A: A lead-acid battery is composed of a series of plates
immerse in a solution of sulfuric acid. Each plate consists of a
grid upon which is attached the active material. All of
the negative plates are connected together, as are all of the
positive plates. When the battery is discharged (when it is
subjected to an electrical load), acid from the electrolyte
combines with the active plate material. This releases energy
and converts the plate material to lead sulfate. The chemical
reaction between constituent parts of the electrolyte and the
spongy lead of the negative plates and The lead dioxide at the
positive plates turns the surface of both plates into lead sulphate. As this process occurs the hydrogen within the acid
reacts with the oxygen within the lead dioxide to form water.
The net result of all this reaction is that the positive plate
gives up electrons and the negative plate gains them in equal
numbers, thereby creating a potential difference between the two
plates. The duration of the reactions producing the cell voltage
is limited If there is no connection between the two plates,
the voltage will remain constant.
Q What is Battery lifetime & how it varies?
A: Rechargeable batteries can be re-charged after they have
been discharged. This is done by applying externally supplied
electrical current, which causes the chemical changes that occur
in use to be reversed. Devices to supply the appropriate current
are called chargers or recharges.
• Plate Thickness
Plate thickness (of the Positive plate) matters because of a
factor called "positive grid corrosion". The positive (+) plate
is what gets eaten away gradually over time, so eventually there
is nothing left - it all falls to the bottom as sediment.
Thicker plates are directly related to longer life. Most
industrial deep-cycle batteries use Lead-Antimony plates rather
than the Lead-Calcium used in AGM or gelled deep-cycle
batteries. The Antimony increases plate life and strength, but
increases gassing and water loss.
• Cycles vs. Life
A battery "cycle" is one complete discharge and recharge
cycle. It is usually considered to be discharging from 100% to
20%, and then back to 100%. Battery life is directly related to
how deep the battery is cycled each time. If a battery is
discharged to 50% every day, it will last about twice as long as
if it is cycled to 80% DOD. If cycled only upto 10% DOD, it will last
about 5 times as long as one cycled to 50%.
• Temperature Effects on Batteries
Battery capacity (how many amp-hours it can hold) is reduced as
temperature goes down, and increased as temperature goes up. The
standard rating for batteries is at room temperature 27 degrees
Celcius. Battery charging voltage also changes with temperature.
Q What is Battery capacity?
A: The capacity of a battery to store charge is often
expressed in ampere hours (1 Ah = 3600 coulombs). If a battery
can provide one ampere (1 A) of current (flow) for one hour, it
has a real-world capacity of 1 Ah. If it can provide 1 A for 100
hours, its capacity is 100 Ah.
Battery manufacturers use a standard method to determine how to
rate their batteries. The battery is discharged at a constant
rate of current over a fixed period of time, such as 10 hours or
20 hours, down to a set terminal voltage per cell. So a 100
ampere-hour battery is rated to provide 5 A for 20 hours at room
temperature. The efficiency of a battery is different at
different discharge rates.
Q Do lead acid batteries discharge when not in use?
A: Yes. All batteries, regardless of their chemistry, will
self-discharge even when no load is present because of its
internal resistance. At a temperature of
27 degrees C, a lead acid battery will self-discharge at a rate
of approximately 4% a week. A battery with a 125 amp-hour rating
would self-discharge at a rate of approximately five amperes per
A rule of thumb is to ALWAYS keep your batteries fully charged
while not in use!
Q Calculating the battery runtime?
A: A battery can either be discharged at a low current over
a long time or at a high current for only a short duration. At
1C, a 10Ah battery discharges at the nominal rating of 10A in
less than one hour. At 0.1C, the same battery discharges at 1A
for roughly 10 hours. While the discharge voltage of lead acid
decreases in a rounded profile towards the end-of-discharge
cut-off. The relationship between the discharge time (in amperes
drawn) is reasonably linear on low loads. As the load increases,
the discharge time reduces because some battery energy is lost
due to internal losses. This results in the battery heating up
Q When should I add water to my batteries?
A: How often you use and recharge your batteries will determine
the frequency of watering? It is best to check your battery
water level frequently and add distilled water when needed.
Never add tap water to your battery. Tap water contains minerals
that will reduce battery capacity and increase their
self-discharge rate. Also never add acid. Only distilled or
de-ionized water should be added to achieve the recommended
Q What is battery Sulphation and when does it occur?
A: Sulphation (or Lead Sulfate) is the formation of hard
crystals on the plates of your battery. Initially, the lead
sulfate coating is soft, thin and easily reconverted into lead
and sulfuric acid when battery is recharged. It is important to
remember, the longer your battery remains discharged, the more
it will begin to form hard crystals of lead sulfate…RECHARGE
YOUR BATTERY AS SOON AS POSSIBLE ALSO IF PLATES ARE DRY!
Q Can I hook different batteries in parallel?
A: When hooking batteries together in parallel, they should
be of identical make and model and similar age.
Q What are the reasons for failure of batteries?
A: Self discharge of plates and premature capacity loss;
excessive float charge current and improper polarization of
plates; shorts through separator, mossing or dendrite growth;
overcharging of battery from high current and subsequent
excessive gassing; excessive heat and loss of water; antimony
transfer; poor charge acceptance; inadequate high rate discharge
Q What is an Equalization Charge & Why it is Necessary?
A: In any cyclic application, a series of batteries will
always need to be equalized from time to time in order to ensure
that the battery cells remain at the same voltage throughout the
pack. During the charge cycle the voltages of the different
batteries will vary. In order to bring them all to the same
level it is necessary to give some a slight overcharge in order
to bring the other up to full charge. Equalization is done by
allowing the voltage to rise while allowing a small constant
current to the batteries. The voltage is allowed to rise above
the normal finish voltage in order to allow the weaker
batteries/cells to draw more current.
Q Are lead acid batteries recyclable?
A: Lead acid batteries are 100% recyclable. The plastic
containers and covers of old batteries are neutralized, reground
and used for manufacturing new battery cases. The
electrolyte can be processed for recycled wastewater uses. In
some cases, the electrolyte is cleaned and reprocessed and sold
as battery grade electrolyte. In other instances, the sulfate
content is removed as Ammonia Sulfate and used in fertilizers.
The separators are often used as a fuel source for the recycling
Q What is the difference between a Cell and a Battery?
A: Strictly, an electrical "battery" is an interconnected
array of one or more similar "cells". A car battery is a
"battery" because it uses multiple cells. Multiple batteries or
cells may also be referred to as a battery pack as a set of
multi-cell 12 V batteries in an electric vehicle. A 12 Volt mono
block battery consists of 6 cells, but a 2 Volt tubular battery
consists of a single cell.
Q Should I take my battery off charge to measure cell
A: No, you should take voltage readings with the battery
stabilized on float charge. This shows whether the charger is
set correctly, and how well the battery is responding to the
charge. Open circuit (off charge) voltage readings are of little
Q What are volts?
A: It is the units of force or pressure of electric
current. The voltage of a battery depends on the number of
cells. Each lead acid cell has 2 volts.
Q What is meant by "specific gravity" of battery electrolyte?
A: It is the weight of the sulfuric acid-water mixture
compared to an equal volume of water. Pure water has a specific
gravity of 1.
Q Why do manufacturers use different alloys in their
batteries (lead-calcium, lead-antimony, lead-selenium, etc.)?
A: The composition of the plate grid alloy can have a major
effect on operating characteristics, such as behavior on float
charging and cycle life. Older lead-antimony designs have good
cycling capability but require frequent water additions,
particularly towards the end of life, due to antimony migration
between the plates. Cells with lead-calcium alloys require far
less watering, but tend to have a poor cycle life. Lead-selenium
alloys are actually low-antimony types with the addition of
selenium as a hardening agent. Such alloys promote good cycling
capability, while maintaining a constant and fairly low level of
water consumption. Many variants on these alloy types are
Q What if the difference between lead-calcium and lead-acid
A: Lead-calcium is one type of lead-acid battery.
Pasted-plate batteries using the lead-acid electrochemistry are
often named for the alloy used for their plate grids.
Q What is the difference between a sealed maintenance-free
battery and a VRLA battery?
A: Not to be confused with maintenance-free car batteries,
so-called 'sealed maintenance-free batteries' were introduced
for stationary applications in the early 80s. While these
batteries are 'sealed' to the extent that there is usually no
access to the inside of the cell, many users misunderstood the
term and installed these batteries in areas with no ventilation.
Such batteries periodically release small amounts of hydrogen in
normal service, and can produce large quantities of this
flammable gas if overcharged. On the maintenance side, it has
been found that these batteries can be unreliable if neglected.
In addition, IEEE has published a recommended practice for
maintaining and testing these batteries.
With these facts in mind, the industry has moved away from the
term, 'sealed maintenance-free' and has agreed on
'valve-regulated lead-acid' (VRLA).
Battery Maintenance Procedure
battery water level such that float on your water level
indicator is above red ring.
Do not add acid.
Do not add tap water.
Top-up only with battery grade distilled water.
Do not spill or over fill battery water.
Ensure battery is charged before use with your inverter or UPS.
Do not expose the battery to rain, excessive moisture or heat.