fact sheet MAY 2003
1002250
Fast charging is a new method that can
recharge electric industrial vehicle batteries
three to six times faster than conventional
charging. Fast charging can save time,
floor space, labor costs and energy. It can
eliminate the need for battery changing
rooms and associated safety hazards in
industrial applications. Fast charging must
still overcome industry misperception
about the technology and its effects on
batteries.
What Is Fast Charging?
As its name implies, fast charging returns
energy to industrial batteries faster than
conventional charging. Whereas conven-
tional chargers are designed to charge
industrial equipment batteries in about
eight hours, fast charging can return a
battery to 80% state-of-charge (SOC) in
about an hour. Several factors affect the
exact recharge time, including the batterys
size, age, type, and condition, its state of
charge, and the chargers power rating.
Fast charging differs from conventional
charging in two important ways:
High current. Fast charging charges a
battery at the highest current rate it
can accept while retaining the maxi-
mum life capability of the battery.
Battery management. Fast charging
preserves battery life by monitoring
battery temperature and/or internal
resistance and adjusting charging cur-
rent as necessary.
The goal of fast charging is threefold:
To reduce the costs associated with
conventional charging. Industrial fast
chargers are typically more expensive
than conventional chargers, but the
savings associated with a fast-charging
regime make them economically effective,
particularly in multi-shift operations.
To help reduce the life cycle cost of
the battery pack by allowing the user to
carefully monitor, manage, and operate
the pack. Most battery manufacturers
agree that fast-charged batteries have
the same ampere-hour throughput as
conventionally charged batteries.
To maximize the operational flexibility
of battery-powered vehicles. Fast charg-
ing provides fast refueling capability
and maintains a batterys SOC in the
40% to 80% range throughout the
workday, eliminating the performance
penalty associated with low SOC at
the end of a work shift, as shown in
Figure 1.
fact sheet
A B C s o f Fa s t C h a r g i n g
Non-Road Electric Transportation Program
Battery State of Charge
100%
80%
60%
40%
20%
Shift 1
Shift 2
Battery
Changing
Fast
Charging
Lunch
Lunch
2:00 pm
10:00 pm
6:00 am
6:00 am

Figure 1. Battery charging in a two-shift operation.
Benefits of Fast Charging
Fast charging can save time,
floor space, labor costs and
energy. It can eliminate the need
for battery changing rooms and
associated safety hazards in
industrial applications
. How Does Fast Charging Work?
A battery is charged by applying current
that reverses the chemical processes that
take place in the battery during discharge.
The rate at which a battery can be charged
depends on how quickly this chemical
reaction can take place. If current is applied
at a higher rate than the battery can con-
vert to stored chemical energy, that sur-
plus energy is dissipated as heat. A given
batterys inherent internal resistance will
also generate heat. Excessive heat buildup
may damage a battery and shorten its life.
A batterys internal resistance changes
with its SOC, temperature, cycling history
and age. Internal resistance is lower when
the SOC is between 20% and 80%. In
this range the battery can most effectively
accept fast charging.
Each fast charger manufacturer imple-
ments its own algorithm to determine the
magnitude of charging current over time.
Some fast chargers also have algorithms for
different battery types, including flooded,
gel and absorbed glass mat (AGM) batteries.
A typical fast charging algorithm will charge
with a high current until the battery reaches
70% to 80% SOC. This current may be
modulated or pulsed with feedback con-
trols from the battery. Thereafter, the
charger holds the voltage level by adjust-
ing charging current, reducing the current
when necessary to avoid overcharging and
subsequent heat buildup. The charger will
either turn off at a specified voltage plateau,
or, time permitting, continue charging at
a slower rate until the battery is fully
charged or equalized, in a manner similar
to a conventional charger.
Conventional Charging Drawbacks
In typical industrial use, an electric vehicle
battery will be depleted to approximately
20% SOC in eight hours or less. Below
20% SOC, vehicle performance degrades,
so 20% SOC is considered the lowest
practical limit for acceptable performance.
In a multi-shift operation, where a vehicle
such as a forklift is required to operate
for two or more shifts in succession, a
depleted battery must be replaced with a
fully charged one at least once each shift.
A typical multi-shift operation needs one
or more batteries per vehicle per shift.
Charging the battery by conventional
methods can take as long as eight hours.
Battery manufacturers typically recommend
an additional cool-down period of as much
as eight hours. At many sites, specially
trained personnel remove depleted batteries
from vehicles and charge them in a dedi-
cated charging room. In a typical 24-hour
period, a battery is in use for only eight
hours, and is maintained in the charging
room for 16 hours.
Conventional charging in a dedicated
charging room is labor intensive, costly,
and introduces safety hazards.
Conventional ChargingLabor Costs
The labor costs associated with conven-
tional battery changing include:
Reduced productivity. It can take as
long as 30 minutes for operators to
drive their vehicles to the charging
room, replace the battery pack, and
return to the floor.
Dedicated battery room personnel.
Operations need full-time, trained
personnel to support the battery room.
Conventional ChargingCapital Costs
The capital costs associated with battery
changing include:
The cost of a dedicated battery room,
which takes up floor space that might
otherwise be used for factory, ware-
house, laboratory, or office space.
The cost of equipment to lift and
transfer batteries from vehicles to
charging racks, and the cost of the
racks themselves.
The cost of extra batteries required for
each vehicle.
Conventional ChargingSafety Hazards
The safety hazards associated with battery
changing include:
The concentration of dangerous fumes
associated with off-gassing of batteries
SuperCharge by Electric Transportation
Engineering Corporation
PosiCharge
®
by AeroVironment, Inc. Fast ChargingEliminates Battery Room
Fast charging eliminates the need for a
dedicated battery changing room and the
personnel required to maintain it. Not
only can the space be converted to pro-
ductive use, the equipment needed to
change batteries is eliminated, freeing
capital for other uses.
Fast ChargingSaves Energy
Fast charging saves energy; the chargers
themselves are more efficient, and battery
overcharge is more controlled. The EPRI
demonstration referenced above revealed
annual savings of $7,467, in energy alone,
for fast charging over conventional charging.
2
Fast ChargingReduces Safety Hazards
Fast charging reduces many of the safety
hazards and accompanying regulations
associated with battery changing. For
example, fast charging eliminates the
OSHA requirement for a wash area
because batteries are not removed from
the vehicles. In addition, because they are
monitored, fast-charged batteries are over-
charged less frequently, thus resulting in
dramatically reduced off-gassing levels.
When off-gassing does occur during
weekly equalization, the amount released
is typically below OSHA/NEC accepted
limits because it is not concentrated in a
battery room.
Challenges to Widespread
Acceptance
Despite the benefits of fast charging, the
industry has yet to completely embrace
the technology. The greatest barrier to
widespread acceptance is industry misper-
ception about the effects of fast charging
on batteries. In addition, some economic
and infrastructure issues remain.
Misperceptions
Research conducted by battery and charger
manufacturers, as well as independent labo-
ratories, has shown that partial discharges
coupled with fast charging need not shorten
battery life. Most battery manufacturers
concur that fast-charged batteries have
the same ampere-hour throughput as
conventionally charged batteries. In addition,
because fast charge operations do not
overcharge batteries as frequently, flooded
lead-acid batteries lose less water from
when they are overcharged, a common
occurrence with conventional charging.
Safety regulations require proper venti-
lation of battery rooms.
Direct handling of batteries, which may
require hazardous materials protocols.
Physical hazards associated with changing
heavy and unwieldy industrial batteries.
Increased cross-plant traffic, particularly
during shift change, as vehicles go to
the battery room for service.
Benefits of Fast Charging
Fast-charging technology provides the
most economic benefit to sites where two
or three eight-hour shifts operate in a
24-hour period.
Fast ChargingIncreases Productivity
Fast charging eliminates battery changing
because batteries are charged in their
vehicles. It increases worker productivity
by eliminating trips to the battery chang-
ing room. In addition, because chargers