Every electrical component in a vehicle is supplied current, from
The battery is a storage device for electrical energy.
The battery also acts as a stabilizer to the voltage for the entire
Most Hybrid vehicles use dual-voltage electrical systems.
The high-voltage system is used to power the electric motor,
while the conventional 12 volt system is used to power all the
other conventional components.
The design of flooded batteries is fairly simple. Negative plates,
made of lead or lead alloy, are sandwiched between positive
plates of a lead alloy.
Plate assemblies are constructed into cells (2.1 volts) and are
placed in a case. The container is then filled with a diluted
sulfuric acid electrolyte.
When Flooded batteries are charging, oxygen gas is generated at
the positive electrode, and hydrogen gas is generated at the
The Hydrogen and Oxygen escape from the cell, requiring water
(distilled) to be replenished from time to time.
NOTE: This is why sparks or open flame near batteries
are dangerous…use caution!
Capacity rate- The period of time and the amount of energy a
battery can supply until discharged to 10.5 volts (12 volt battery)
Amp Hours- Is a unit of measure calculated by multiplying the
amount of electrical current a battery will deliver (amps) by the
time in which it will deliver current (time) until the battery
reaches a terminal voltage of 10.5 (12 volt battery)
For example; a 60Ah battery delivers 60 amps for 1 hour.
Cold Cranking Amps- The number of amps that can be supplied
by a battery at 0 degrees Fahreinheit.
Cranking Amps- The number of amps that can be supplied by a
battery at 32 degrees Fahrenheit.
Reserve Capacity- The number of minutes for which the battery
can produce 25 amps and still have a battery voltage of 10.5
volts. (The time a vehicle can be driven in the event of a
charging system failure)
NOTE: The voltage of a battery does not necessarily
indicate whether the battery can perform, but it does
indicate overall condition.
1. Determine the CCA (The proper test is performed at one-half
the CCA rating).
2. Connect load tester
3. Apply load for 15 seconds and observe the voltmeter during the
load testing. Check voltage at the end. (should be above 9.6V)
4. Repeat test for accuracy.
NOTE: If the battery has just been charged or the vehicle
has been driven, it is necessary to remove the surface
charge before testing. To do this, turn on headlights for
one minute, then off for two minutes.
Conductance test is a measure of how well a battery can create
current. This tester sends a small AC signal through the battery and
then measures part of the AC response (phase). As the battery ages
the plates can become sulfated and shed active materials from the
grid, reducing the battery capacity. (measures internal resistance)
1. Hook up tester to battery (make sure connections are clean)
2. Enter CCA rating
3. Results are displayed
Determine the charge rate by
comparing the state of charge
(SOC) to the table.
Note: AGM batteries require
special chargers and operate
at less than 14.4 volts.
The capacity of batteries change with temperature. The lower
the temperature the lower the capacity. The maximum
temperature a battery can operate without significantly
damaging cell plates is 140 degrees Fahrenheit. (paint booth)
Manufactures design thermal systems that can either warm or
cool batteries to maintain optimum capacity.
Make sure all accessories are off, and ignition keys are out of
Check to make sure all doors are “closed” and dome light is off.
Disconnect negative battery terminal and install a parasitic load
Start the engine and drive the vehicle about 10 minutes, being
sure to turn on all lights and accessories.
Turn the engine and all accessories off, and remove ignition key
from the vehicle.
Connect an ammeter across the parasitic load tool, and open
tool switch. Wait at least 20 min. (hour on some vehicles)
Acceptable limit is 50mA
Or use an inductive clamp
ammeter measurement tool
Yes you can, and still need to jump start hybrid vehicles. The 12
Volt system is responsible for turning on the high-voltage
system. If the 12 volt system is discharged, it can be jump
started just like any other conventional system.
Check with manufacture service procedures (they can differ).
The last connection made, should always be on the dead vehicle
and connected to the ground side (engine block) to eliminate
danger from spark.
Rechargeable nickel-metal hydride NiMH batteries are dominant
for several reasons
1. High electrolyte conductivity permits high power applications.
2. Battery system is sealed to minimize maintenance and leakage
3. Operates over wider temperature range
4. Can deliver high energy density
5. Materials are plentiful and recyclable.
6. Electrolyte does not enter into the cell reaction, which produces
high power and long life. (3 times the energy of PbA)
Positive electrode is made of nickel hydroxide, and the negative
electrode is made of a hydrogen absorbing alloy called “metal
NiMH batteries are called alkaline storage batteries because of
the use of alkaline potassium hydroxide electrolyte (instead of
Although NiMH batteries use nontoxic materials, they are still
corrosive and caution should be taken not to get electrolyte on
the skin or eyes.
They are constructed in two different ways;
1. Cylindrical- Similar to “D” cell batteries, grouped into modules
that are six cells connected in series. The groups are then
connected in series to each other. (well over 100 volts)
2. Prismatic- Similar to conventional 12 volt cells, they are
rectangular or boxlike, formed into flat plates. Each plate consists of
6 cells (series) and are then connected in series. (over 200 volts)
Lithium Ion- Used by Tesla, Toyota (PHEV), Chevy Volt, and
Nissan Leaf. Lithium ion batteries are cylindrical, and contain
twice the energy of NiMH. These batteries require special
charge and cooling management, are expensive and prone to
Nickel-Cadmium (Ni-Cd)- Similar to NiMH, Ni-Cd uses alkaline
electrolyte but different electrode alloys.
Lithium Polymer (Li-poly)- Use a solid state electrolyte, but
operate at high temperatures (safety)
Zinc-Air- Uses a sacrificial negative electrode made of Zinc and
must be replaced to be recharged.
ZEBRA- A sodium-metal-chloride battery that uses two different
types of electrolytes. Also operates at high temperatures.
Most hybrid/electric vehicles use a cooling fan that distributes
heated or cooled air past the HV electronics and battery.
Proper airflow must move past the HV components.
Some vehicles like Ford use the air-conditioning system to cool
the high-voltage components, and the heating system to heat
them up. (Using water heat exchangers)
Temperature sensors are mounted in various locations in the
battery pack housing to send data to the module responsible for
controlling battery temperature. May be under battery as shown
below. (Toyota put temperature sensors under the battery on
some Prius’s’s’s’s, and on top of the battery on others?)
Although the vehicle only monitors a few temperature sensors
in various locations, it monitors the voltage of each cell block
(around 7.2 volts). This is a good spot to check for corrosion and
increased resistance. (wear gloves)
The equivalent of a fuel gauge for electric/hybrid vehicles.
Can’t determine by voltage alone, must also compare amperage
and temperature to determine overall charge stored.
The high-voltage battery in a hybrid or electric vehicle is
subjected to constant charging and discharging during normal
operation. The battery can overheat under the following
1. The battery state of charge SOC is above 80%
2. The battery is placed under a load with its SOC below 20%
In order to prevent overheating and maximize service life, the
battery SOC must be carefully managed. Most hybrids and
electric vehicles target SOC of 60% (range from 40% to 60%)
This allows for regenerative braking to maximize efficiency up to
the 80% SOC and keeps battery high enough to diagnose no
start ICE faults and operate in EV mode longer.
NOTE: Hybrid batteries have
a higher self discharge rate,
and long term storage
(month) can damage the
battery behind repair.
Drive vehicle for at least 30
minutes per month!
During normal vehicle operation, the high-voltage battery is
monitored by the control module. This module monitors battery
temperature, current, and voltage to calculate SOC. It uses this
information to determine the correct rate of charge.
When the SOC drops below its threshold (usually 50% ish) the
ICE starts to recharge the high-voltage batteries. (idle stop is
disabled when SOC is low)
If SOC reaches above 80% regenerative braking stops. This
means that during braking a harder than normal brake pedal
effort is noticed.
If a hybrid owner complains of lack of power on acceleration,
check the SOC first. There may be nothing wrong with the
traction motor or ICE. It maybe the high-voltage battery pack is
not within normal SOC causing power output to be less.
Connecting batteries in series requires the batteries be close to
the same voltage. Series connected batteries receive the same
charge-discharge current, and an out of range cell will never
match on its own. (1.2 volt variance allowed between blocks)
Although the vehicle is the BEST charger for high-voltage
batteries, there are times when we need to charge individual
cells. Follow these steps.
1. Safely de-energize the vehicle according to manufacture
2. Disassemble wiring to individual cells (isolating them)
3. Check the voltage of each cell
4. Do not use cells that are below 5.4 volts (10.8 for block)
5. If cells are below 7.5 but above 5.4, charge at a maximum of 16
volts at 2 to 6 amps.
6. Monitor battery temperature and do not allow the battery to
overheat (120 degrees Fahrenheit)
7. Allow the voltage to stabilize after being charged. Then record
the no load voltage.
8. Use a high wattage resistor to apply a load to the batteries. (1.5
ohm resistor rated at 25 Watts)
9. Apply the load resistor and measure the new voltage and current
We will use these measurements to determine internal resistance.
(internal resistance will cause low voltage when under load and
high voltage when being charged, greater delta difference)
Manufacture grid chargers can discharge, and
recharge/rebalance the battery pack, if you have $30K!
Technicians will sometimes measure all cells and discharge them
all to the lowest cell, as long as its above 20% SOC.
To determine the internal resistance of a block, compare the
unloaded voltage to the loaded voltage, this is your delta or
“change” in voltage.
The difference is divided by the measured current during the
For example, if the current was 9.6 amps and your difference
was .29 volts;
Ideally we would like close to zero but try to match them as close as
possible. (25 to 35 is average, with 15 to 40 milliohms the spec)
Besides crucial DTC’s, there are SEVERAL helpful data pids
accessible from the scan tool. For example;
1. Battery Temperature
2. Battery voltage
3. Cell voltage
4. State of Charge
5. Delta State of charge
6. Battery Current Draw
7. Internal Resistances
8. Cooling fan/heater operation
High-Voltage vehicles are equipped with a safety disconnect
switch, that is used to cut off high voltage from the rest of the
system beyond the battery pack.
Used EVERY time ANY high-voltage service work is done.
The location and type of disconnect switch varies from
manufacture to manufacture. Always check service procedure.
To safely depower the high-voltage system, always follow
manufacture service information. Steps usually include;
1. Turn the ignition off and remove key from the vehicle (store in
lock box at least 15 feet away)
2. Remove the 12 volt power source to the high-voltage system.
(Usually a fuse or relay, but I would disconnect the battery)
3. Remove the high-voltage service plug, and store in lock box
with ignition key/fob. (or turn it off for Honda)
NOTE: Even if all the above steps are performed, there is still a risk for
electrical shock at the battery module and capacitors. Make sure
capacitors are drained and proceed with caution when removing battery,
using high voltage gloves.
Notice again how the disconnect switch just opens up a series
connection between two blocks, separating the battery into two
lower voltage sections. (Voltage is still present in battery)
Electric motors use large amounts of electrical power. If a low
voltage system was used, the cables and electric motor would
have to be HUGE!
Remember OHMS Law!
OHM’s law applies to power also, which is measured in WATTS
Power(WATTS)=Amps X Volts
So if we need a certain Watt to power the electric motor….
and Watts are equal to Amps multiplied by Volts…..then
What happens if voltage decreases?
How do we maintain Watts?
Lets take a look at an example, using a 10kw electric motor (IMA)
In this example we see that a 10kW motor operated at 200 Volts
needs 50 Amps. So what happens if we drop the voltage to 14!
How would this effect the cable size?
Used as a first line of “defense” for safety to isolate High-Voltage
in the battery from the rest of the vehicle.
Electromagnetic relay controlled by the 12 volt system
High-Electric systems use at least two relays, and sometimes
three, that are activated/deactivated based on system criteria.
Three relays are used to limit current arc. SMR3 and SMR1 are
energized. (note resistor in SMR1 circuit, this limits current)
Next SMR2 energizes and completes the High-Voltage floating
Newer Hybrids moved the pre-charge relay to the ground side.
High-Voltage interlocks are located on the high-voltage system
to check for tampering or unplugged connections in the High-
Used as a extra safety point to power down the high-voltage
system in the event of damage, tampering, or removal of parts.
Composed of a single wire that runs in and out of connectors,
and covers, when open, sends a signal to the control module.
Since DC just keeps on producing current, hybrids require a
special high-voltage DC fuse.
Built with a special material inside that creates a non-conductive
gas internally, quenching the arc.
Usually built into the switch.