This document provides an overview of electric vehicle batteries, including: 1. A brief history of batteries and their use in early electric vehicles. 2. The key requirements for EV batteries including safety, high power, high capacity, small size, long life, and low cost. 3. The types of batteries used in EVs including lead-acid, lithium-ion, nickel-based, and others. 4. Factors that affect battery performance and safety such as temperature, charging, and battery management systems.

1. Electric Vehicle Batteries
North Bay Chapter of the Electric Auto Association
www.nbeaa.org
Updated 8/14/09
Posted at: http://www.nbeaa.org/presentations/batteries.pdf

2. NBEAA 2009 Technical Series
1. EV Drive Systems
TODAY >> 2. EV Batteries
3. EV Charging Systems
4. EV Donor Vehicles

3. Agenda
What is a Battery?
Battery History
EV Battery Requirements
Types of EV Batteries
EV Battery Temperature Control
EV Battery Charging
EV Battery Management
EV Battery Comparison
EV Record Holders
Future EV Batteries
EV Drive System Testimonials, Show and Tells and Test Drives

4. What is a Battery?
electrolyteanode + cathode -
charger
current
During Charge
voltage and energy increases
energy
heat
heat
chemical
reaction

5. What is a Battery?
electrolyteanode + cathode -
load
current
During Discharge
voltage and energy decreases
work
heat
heat
chemical
reaction

6. Battery History
Rechargeable batteries highlighted in bold.
First battery, “Voltaic Pile”, Zn-Cu with NaCl electrolyte, non-
rechargeable, but short shelf life
1800 Volta
First battery with long shelf life, “Daniel Cell”, Zn-Cu with
H2SO4 and CuSO4 electrolytes, non-rechargeable
1836 England John Fedine
First electric carriage, 4 MPH with non-rechargeable
batteries
1839 Scotland Robert Anderson
First rechargeable battery, “lead acid”, Pb-PbO2 with
H2SO4 electrolyte
1859 France Gaston Plante
First mass produced non-spillable battery, “dry cell”, ZnC-
Mn02 with ammonium disulphate electrolyte, non-
rechargeable
1896 Carl Gassner
Ni-Cd battery with potassium hydroxide electrolyte
invented
1910 Sweden Walmer Junger
First mass produced electric vehicle, with “Edison
nickel iron” NiOOH-Fe rechargeable battery with
potassium hydroxide electrolyte
1914 US Thomas Edison and
Henry Ford
Modern low cost “Eveready (now Energizer) Alkaline” non-
rechargeable battery invented, Zn-MnO2 with alkaline
electrolyte
1955 US Lewis Curry
NiH2 long life rechargeable batteries put in satellites 1970s US
NiMH batteries invented 1989 US
Li Ion batteries sold 1991 US
LiFePO4 invented 1997 US

7. EV Battery Requirements
Safe
High Power
High Capacity
Small and Light
Large Format
Long Life
Low Overall Cost

8. EV Battery Requirements: Safe
Examples of EV battery safety issues:
Overcharging
explosive hydrogen outgassing
thermal runaway resulting in melting, explosion or inextinguishable fire
Short Circuit
external or internal
under normal circumstances or caused by a crash
immediate or latent
Damage
liquid electrolyte acid leakage

9. EV Battery Requirements: High Power
Power = Watts = Volts x Amps
Typically rated in terms of “C” – the current ratio between max current and
current to drain battery in 1 hour; example 3C for a 100 Ah cell is 300A
Battery voltage changes with current level and direction, and state of charge
1 Horsepower = 746 Watts
Charger efficiency = ~90%
Battery charge and discharge efficiency = ~95%
Drive system efficiency = ~85% AC, 75% DC
batteries motor
controller
motor
heat heat heat
shaftcharger
heat
100% in 60% - 68% out32% - 40% lost to heat

10. EV Battery Requirements: High Power
Example
Accelerating or driving up a steep hill
Motor Shaft Power = ~50 HP or ~37,000 W
Battery Power = ~50,000 W DC, ~44,000 W AC
Battery Current
~400A for 144V nominal pack with DC drive
~170A for 288V nominal pack with AC drive
Driving steady state on flat ground
Motor Shaft Power = ~20 HP or ~15,000 W
Battery Power = ~20,000 W DC, ~18,000 AC
Battery Current
~150A for 144V nominal pack with DC drive
~70A for 288V nominal pack with AC drive
Charging
Depends on battery type, charger power and AC outlet rating
Example: for 3,300 W, 160V, 20A DC for 3,800 W, 240V, 16A AC

11. EV Battery Requirements: High Capacity
Higher capacity = higher driving range between charges
Energy = Watts x Hours = Volts x Amp-Hours
Watt-hours can be somewhat reduced with higher discharge current due to internal
resistance heating loss
Amp-Hours can be significantly reduced with higher discharge current seen in EVs
due to Peukert Effect
Amp-Hours can be significantly reduced in cold weather without heaters and insulation
Example:
48 3.2V 100 Amp-Hour cells with negligible Peukert Effect and 95% efficiencies
Pack capacity = 48 * 3.2 Volts * 100 Amp-Hours * .95 efficiency = 14,592 Wh
340 Watt–Hours per mile vehicle consumption rate
Vehicle range = 14,592 Wh / 340 Wh/mi = 42 miles

12. EV Battery Requirements: Small and Light
Cars only have so much safe payload for handling and reliability
Cars only have so much space to put batteries, and they can’t go anywhere
for safety reasons
Specific Power = power to weight ratio = Watts / Kilogram
Specific Energy = energy capacity to weight ratio = Watt-Hours / Kilogram
Power Density = power to volume ratio = Watts / liter
Energy Density = energy to capacity to volume ratio = Watt-Hours /liter
1 liter = 1 million cubic millimeters
Example:
1 module with 3,840 W peak power, 1,208 Wh actual energy, 15.8 kg, 260
x 173 x 225 mm = 10.1 liters
Specific Power = 3,840 W / 15.8 kg = 243 W/kg
Specific Energy = 1,208 Wh / 15.8 kg = 76 Wh/kg
Power Density = 3,840 W / 10.1 l = 380 W/l
Energy Density = 1,208 Wh / 10.1 l = 119 Wh/l

13. EV Battery Requirements
Large Format
Minimize the need for too many interconnects; example 100 Ah
Long Life
Minimize the need for battery replacement effort and cost
Example: 2000 cycles at 100% Depth-of-Discharge to reach 80% capacity
charging at C/2; 5 years to 80% capacity on 13.8V float at 73C
Low Overall Cost
Minimize the purchase and replacement cost of the batteries
Example: $10K pack replacement cost every 5 years driven 40 miles per
day down to 80% DOD = 1825 days, 73,000 miles, 14 cents per mile

14. Source: Life Expectancy and Temperature, http://www.cdtechno.com/custserv/pdf/7329.pdf.
Higher Temperature Reduces Shelf Life
13 degrees reduces the life of lead acid batteries by half.

15. EV Battery Comparison
Type Power Energy Stability
Max
temp Life Toxicity Cost
LiFePO4 + + + ~ ~ + -
LiCO2 + + - - - + -
NiZn ~ ~ ~ ~ - + ~
NiCd - ~ ~ ~ + - +
PbA AGM + - + ~ - - +
PbA gel ~ - + ~ - - +
PbA flooded ~ - - ~ - - +
Available large format only considered; NiMH, small format
lithium and large format nano lithium not included.

17. Data Source: MPS 12-75 Valve Regulated Lead Acid Battery Datasheet,
http://www.cdstandbypower.com/product/battery/vrla/pdf/mps1275.pdf.
Note: do not use Dynasty MPS batteries in EVs – they are not designed for
frequent deep cycling required in EVs
Peukert Effect
Dynasty AGM MPS Series 75 Ah
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 50 100 150 200 250
Constant Discharge Rate, Amps
Amphoursto80%DOD(1.75VPC,10VP6C)
Lead Acid Battery “Peukert” Effect Reduces Range at EV Discharge Rates
A “75 Amp Hour” battery that provides 75 amp hours at the 20 hour C/20 rate or 3.75
amps only provides 42 amp-hours at 75 amps, a typical average EV discharge rate, or
57% of the “nameplate” rating. Nickel and lithium batteries have far less Peukert
effect.

18. Source: Dynasty VRLA Batteries and Their Application,
http://www.cdtechno.com/custserv/pdf/7327.pdf.
Lead Acid AGM Batteries are Better for High Current Discharge Rates
Gels have higher internal resistance.
Higher discharge rates are typical in heavier vehicles driven harder in higher gears
with smaller packs and less efficient, higher current, lower voltage DC drive systems.

19. Source: Impedance and Conductance Testing,
http://www.cdtechno.com/custserv/pdf/7271.pdf.
Source: Capacity Testing of Dynasty VRLA
Batteries,
http://www.cdtechno.com/custserv/pdf/7135.pdf.
Lead Acid Batteries Need Heaters in Cold Climates
They lose 60% of their capacity at 0 degrees Fahrenheit.

20. Source: Dynasty VRLA Batteries and Their Application,
http://www.cdtechno.com/custserv/pdf/7327.pdf.
Gels Have a Longer Cycle Life
AGMs only last half as long, but as previously mentioned can withstand higher discharge rates.

21. Flooded Lead Acid Battery Acid Containment is Required for Safety
In addition to securing all batteries so they do not move during a collision or rollover, flooded
lead acid batteries need their acid contained so it does not burn any passengers.

22. Flooded Lead Acid Battery Ventilation is Required for Safety
When a cell becomes full, it gives off explosive hydrogen gas. Thus vehicles and their garages
need fail safe active ventilation systems, especially during regular higher equalization charge
cycles that proceed watering.

23. High Power, High Capacity Deep Cycle Large Format Batteries Used in EVs:
LiFePO4 Hi Power
Thunder Sky LMP
Valence Technologies U-Charge XP, Epoch
PbA AGM BB Battery EVP
Concorde Lifeline
East Penn Deka Intimidator
EnerSys Hawker Genesis, Odyssey
Exide Orbital Extreme Cycle Duty
Optima Yellow Top, Blue Top
Gel East Penn Deka Dominator
Flooded Trojan Golf & Utility Vehicle
US Battery BB Series
NiCd Flooded Saft STM
NiZn SBS Evercel
Li Poly Kokam SLPB
Note: LiFePO4 are recommended, having the lowest weight but highest initial
purchase price. But they have similar overall cost, and the rest have safety, toxicity or
power issues.

24. EV Battery Charging

25. Source: Charging Dynasty Valve Regulated Lead Acid Batteries,
http://www.cdtechno.com/custserv/pdf/2128.pdf.
Battery Chargers Need Voltage Regulation and Current Limiting
This shortens charge time without shortening life.

26. Source: Thermal Runaway in VRLA Batteries – It’s Cause and Prevention,
http://www.cdtechno.com/custserv/pdf/7944.pdf.
EV Charger Temperature Compensation is Required for Safety
Excess voltage at higher temperatures can lead to thermal runaway, which can melt lead
acid modules, explode nickel modules, and ignite thermally unstable lithium ion cells.
Battery cooling systems are typically employed with nickel and unstable lithium ion packs
to maintain performance while providing safety.

27. EV Battery Management

28. EV Batteries Need to be Monitored
• All batteries need to be kept within their required voltage and temperature ranges for
performance, long life and safety. This is particularly important for nickel and thermally unstable
lithium ion batteries which can be dangerous if abused.
• Ideally each cell is monitored, the charge current is controlled, and the driver is alerted when
discharge limits are being approached and then again when exceeded.
• For high quality multi-cell modules without cell access, module level voltage monitoring is
better than no monitoring.
• For chargers without a real time level control interface, a driven disable pin or external
contactor will suffice for battery protection, but may result in uncharged batteries in time of need.
• Dashboard gages and displays are good, but combining them with warning and error lamps is
better.

29. Data Source: Integrity Testing,
http://www.cdtechno.com/custserv/pdf/7264.pdf.
Internal Resistance Effect
10.0
10.5
11.0
11.5
12.0
12.5
13.0
0 100 200 300 400 500 600
discharge rate, ampsbatteryvoltage
Dynasty 12-75 AGM (4.5 milliohm)
Data Source: MPS 12-75 Valve Regulated Lead
Acid Battery Datasheet,
http://www.cdstandbypower.com/product/battery/vrl
a/pdf/mps1275.pdf.
Amp-Hour Counters are More Accurate “Fuel Gages” Than Volt Meters
Open circuit voltage drops only 0.9V
between 0 and 80% depth of
discharge.
Voltage drops up to 2.7V at 600 amps
discharge, and can take a good part of
a minute to recover.
Open Circuit Rest Voltage vs. Depth of Discharge
10.0
10.5
11.0
11.5
12.0
12.5
13.0
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Depth of Discharge
6cellRestVoltage
AGM
Gel
Ideally your fuel gage looks at all of the above plus temperature and then estimates
depth of discharge.
To predict when your batteries will drop below the minimum voltage, Depth of
Discharge should be monitored.
Note: do not use Dynasty MPS batteries in EVs – they are not designed for
frequent deep cycling required in EVs

30. EV Batteries Need to be Balanced
• All batteries will drift apart in state of charge level over time. This is due to differences in
Peukert effect and internal leak rates. This will be detected during monitoring as early low
voltages during discharge, and early high voltages and not high enough voltages during charge.
• Sealed batteries need to be individually balanced, whereas flooded batteries can be
overcharged as a string, then watered.
• Individual balancing can be done manually on a regular basis with a starter battery charger, or
with a programmable power supply with voltage and current limits, but the latter can be
expensive. And it can be a hassle, and it can be difficult if the battery terminals are hard to get
to.
• Automatic balancing maximizes life and performance. Ideally balancing is low loss, switching
current from higher voltage cells to lower voltage cells at all times. Bypass resistors that switch
on during finish charging only is less desirable but better than no automatic balancing.

31. EV Battery Pictures

32. Optima Blue Top AGM Sealed Lead Acid Batteries with PCHC-12V-
2A Power Cheqs Installed in Don McGrath’s Corbin Sparrow

33. Valence Module

34. Valence BMU

35. Valence batteries and BMU connected via RS485

36. Valence battery monitoring via CANBus and USB to laptop

37. Valence Cycler 2.4 battery monitoring screen capture (idle mode; 2.8
now available)

38. Valence battery monitoring file list

39. Valence battery monitoring file example

40. Valence battery monitoring results: maximum charge voltage vs. target
Troubleshooting unbalanced cell (dropped from >90 Ah to 67 Ah after balancing
disabled for 3 months due to late onset RS485 errors due to missing termination
resistor and unshielded cables)

41. Valence battery monitoring results: discharge

42. Valence battery monitoring results: charge and discharge
Troubleshooting bad cell that abruptly went from >90 Ah to 25 Ah in less than 1 week

43. EV Record Holders
AC Propulsion tZero: drove 302 miles
on a single charge at 60 MPH in 2003,
Lithium Ion batteries
Phoenix Motorcars SUT: charged 50
times in 10 minutes with no
degradation in 2007; 130 mile range
Solectria Sunrise: drove 375 miles on a
single charge in 1996, NiMH batteries
DIT Nuna: drove 1877 miles averaging 55.97
MPH on solar power in 2007, LiPo batteries

44. Future EV Batteries
Stanford University Silicon Nanowire
electrodes have 3X capacity
improvement expected for Lithium
batteries
Not technically a battery, but MIT
Nanotube ultracapacitors have very
high power, 1M+ cycle energy
storage approaching Lithium battery
capacity