MK Battery Manual

11
Follow these tips for the longest life:
• Avoid ultra-deep discharges.
• Don’t leave a battery at a low stage of charge for an extended
length of time. Charge a discharged battery as soon as possible.
• Don’t cycle a battery at a low state of charge without regularly
recharging fully.
• Use the highest initial charging current available (up to 30%
of the 20-hour capacity per hour) while staying within the
proper temperature-compensated voltage range.
Why can’t EPM VRLA batteries be
discharged too low?
Our VRLA batteries are designed to be “acid-starved.” This means
that the power (sulfate) in the acid is used before the power in the
plates. This design protects the plates from ultra-deep discharges.
Ultra-deep discharging is what causes life-shortening plate shedding
and accelerated positive grid corrosion which can destroy a battery.
Why does temperature have such
a dramatic effect on batteries?
Temperature is a major factor in battery performance, shelf life,
charging and voltage control. At higher temperatures there is
dramatically more chemical activity inside a battery than at lower
temperatures. The following charts graphically illustrate this fact.
Typical Self-Discharge of VRLA Batteries
at Different Temperatures
AGM Charge and Float Voltages
at Various Temperature Ranges
Gel Charge and Float Voltages
at Various Temperature Ranges
What is acid stratification?
How do VRLA batteries prevent it?
See page 6 for a detailed explanation of this phenomenon.
How does a battery recharge?
The process is the same for all types of lead-acid batteries: flooded,
gel and AGM. The actions that take place during discharge are the
reverse of those that occur during charge.
The discharged material on both plates is lead sulfate (PbSO
4
).
When a charging voltage is applied, charge flow occurs. Electrons
move in the metal parts; ions and water molecules move in the elec-
trolyte. Chemical reactions occur at both the positive and negative
plates converting the discharged material into charged material. The
material on the positive plates is converted to lead dioxide (PbO
2
);
the material on the negative plates is converted to lead (Pb).
Sulfuric acid is produced at both plates and water is consumed at
the positive plate.
If the voltage is too high, other reactions will also occur. Oxygen is
ripped from water molecules at the positive plates and released as
a gas. Hydrogen gas is released at the negative plates—unless,
oxygen gas can reach the negative plates first and “recombine” into
H
2
O.
A battery will
“ gas” near the end of charge because the charge
rate is too high for the battery to accept. A temperature-compensat-
ing, voltage-regulating charger, which automatically reduces
the charge rate as the battery approaches the fully charged state,
eliminates most of this gassing. It is extremely important
not to charge batteries for long periods of time at rates which
cause them to gas because they use water, which in sealed valve-
regulated batteries cannot be replaced. Of course, no battery should
be overcharged for a long period of time…even at low rates using
so-called “trickle charges.”
In a fully charged battery, most of the sulfate is in the sulfuric acid.
As the battery discharges, some of the sulfate begins to form
on the plates as lead sulfate (PbSO
4
). As this happens, the acid
becomes more dilute, and its specific gravity drops as water
replaces more of the sulfuric acid. A fully discharged battery has
more sulfate in the plates than in the electrolyte.
The following illustration shows the relationship between specific
gravity readings and the combination of the sulfate from the acid
with the positive and negative plates at various states of charge.
25
50
75
100
STORAGE TIME (MONTHS)
0369121518212427
40°C
104°F
30°C
86°F
20°C
68°F
8°C
46°F
% RATED CAPACITY AVAILABLE
Temp. Charge Float Temp.
°F Optimum Maximum Optimum Maximum °C
≥ 120 13.60 13.90 12.80 13.00 ≥ 49
110 – 120 13.80 14.10 12.90 13.20 43 – 49
100 – 110 13.90 14.20 13.00 13.30 38 – 43
90 – 100 14.00 14.30 13.10 13.40 32 – 38
80 – 90 14.10 14.40 13.20 13.50 27 – 32
70 – 80 14.30 14.60 13.40 13.70 21 – 27
60 – 70 14.45 14.75 13.55 13.85 16 – 21
50 – 60 14.60 14.90 13.70 14.00 10 – 16
40 – 50 14.80 15.10 13.90 14.20 4 – 10
≤ 40 15.10 15.40 14.20 14.50 ≤ 4
Temp. Charge Float Temp.
°F Optimum Maximum Optimum Maximum °C
≥ 120 13.00 13.30 12.80 13.00 ≥ 49
110 – 120 13.20 13.50 12.90 13.20 44 – 48
100 – 109 13.30 13.60 13.00 13.30 38 – 43
90 – 99 13.40 13.70 13.10 13.40 32 – 37
80 – 89 13.50 13.80 13.20 13.50 27 – 31
70 – 79 13.70 14.00 13.40 13.70 21 – 26
60 – 69 13.85 14.15 13.55 13.85 16 – 20
50 – 59 14.00 14.30 13.70 14.00 10 – 15
40 – 49 14.20 14.50 13.90 14.20 5 – 9
≤ 39 14.50 14.80 14.20 14.50 ≤ 4