1. Battery Basics A guide to battery use in engineering projects
Thomas G. Cleaver University of Louisville Department of Electrical and Computer Engineering Nov. 14, 2016

2. References
This presentation was developed using the following sources:
T.E. Bell, “Choosing the Best Battery for Portable Equipment,” IEEE Spectrum, March, 1988, pp
Walt Kester, Joe Buxton, “SECTION 5, BATTERY CHARGERS,” available at
Custom Power Solutions, available at
New Technology Batteries Guide (1998), available at
Green Batteries, available at
Steve Garland, Kyle Jamieson, “Battery Overview,” available at:
Harding energy Inc, available at
BatteryUniversity.com, available at

3. Battery Terms 1
Capacity: The charge a battery can hold in ampere-hours (Ah) or milliampere-hours (mAh) or the energy the battery can hold in watt-hours.
C: Charge or discharge rate. Battery capacity in Ah or mAh divided by 1 hour. Also know as C rate.
Charge life: The total capacity over the life of the battery (capacity x cycles).
Discharge rate: The maximum allowable load or discharge current.
End voltage: The voltage below which a battery will not operate satisfactorily. Also know as “final voltage.”
Energy density: The energy storage capacity of a battery compared to its mass or volume. The higher the energy density, the better.
Memory effect: The tendency of some rechargeable batteries to lose capacity when not periodically totally drained – a particular problem in NiCd batteries.
Capacity – e.g mAh – Important
Example: iPhone battery is rated at 1440 mAh (depending on iPhone model)
C: Some batteries are rated for maximum current at, say, 2C.
End voltage – Alkaline batteries start at 1.5 V. End voltage is .8 V.
Energy density – So far, Li-ion is the best.

4. Battery Terms 2 Primary battery: A disposable battery.
Polarity reversal: The reversal of the polarity of an over-discharged cell of a rechargeable battery in a series connection. If one cell in a series string discharges before the others, the discharged cell may reverse polarity. If the current is maintained, the reversed cell may be permanently damaged.
Secondary battery: A rechargeable (storage) battery.
Self-discharge: The loss of charge over time of a battery when it is unused.
Service life: The length of time a battery is expected to be usable.
Shelf life: The length of time a battery will retain useful charge when stored.
Polarity reversal – So when the voltage is low (for rechargeables), it’s time to recharge.
Service life – Things that shorten service life:
There are 2 things that shorten the life of a Li-ion battery, like you have in your cell phone: Charging too soon/too often, and charging too late (deep discharge).
Charge/discharge cycles. Batteries can only go through a certain number of charge/discharge cycles before they go bad. It’s about 1000 cycles for Li-ion. So don’t recharge your phone every night, and don’t leave your laptop plugged in all the time.
Deep discharge of Li-ion batteries. So don’t let your phone or laptop completely drain.
Smartphone battery buying guide: “Industry experts suggest charging smartphones when only 40% of battery life is left. They also suggest charging to only 80% charge.
Service life is 2-3 years for Li-ion.
Shelf life – Related to self discharge. Alkalines have long shelf life (a few years).
NiCd 15-20%/yr
NiMH 30%/yr
SLA 5%/yr
Li-ion 3%/yr

5. Primary (Disposable) Battery Types
Zinc-carbon:
“Ordinary” battery
Voltage decreases steadily during discharge
Zinc-alkaline:
“Alkaline” battery
Better than zinc-carbon
Zinc-air:
Button cell hearing aid batteries
Voltage almost constant over useful life
Lithium ion:
High energy density
Zinc-carbon – Frequently advertised as “heavy duty.” That’s BS. They are the lightest duty.
Zinc-alkaline – Zinc-carbon and zinc-alkaline batteries have a nominal voltage of 1.5 V, but this is just the voltage of the battery when it’s fresh. Voltage will drop off with use.
Lithium ion – Yes, there are non-rechargeable Li-ion batteries. They have long shelf life.

6. Secondary (rechargeable) Battery Types
Sealed Lead-Acid (SLA):
Automobile batteries
Low cost
Lead is toxic; sulfuric acid is corrosive.
Nickel-Cadmium (NiCd):
Inexpensive
Memory effect
Cadmium is toxic.
Nickel-metal-hydride (NiMH):
Moderately expensive
Voltage almost constant over useful life
Lithium ion (Li-ion):
Expensive
High energy density
Dangerous if overcharged
Sealed lead-acid – Cheap. Most bang for the buck. Nominal 2 V.
NiCd –Pretty cheap. Not used much anymore. Nominal 1.2 V. Electronic tooth brush.
NiMH – A little more expensive. Nominal 1.2 V. Used in Prius hybrid. Twice the energy density of NiCd.
Li-ion – Most expensive. Best energy density. Nominal 3.6 V. Used in laptops, mobile phones, Chevy Volt hybrid, and Tesla. Burning laptop. Fire on Boeing 787. exploding E cigarette. Samsung Galaxy Note 7

7. Standard Sizes
Button – used in hearing aids and in other applications that require small size
Cylindrical – like AAA, AA, C, D – all usually 1.2 to 1.5 V
Prismatic – like 9 V batteries
Rechargeable Li-ion does not typically come in standard cylindrical sizes.
Button – Size of a dime or smaller.
Prismatic – Cut open a 9 V alkaline battery. You’ll find 6 small 1.5 V batteries in series.
Rechargeable Li-ion – Not available in standard sizes because of danger of putting one in the wrong kind of charger, which may cause a fire. Li-ion chargers incorporate over-voltage protection. Primary Li-ion batteries are cylindrical.

8. Discharge and Voltage
The voltage of some batteries doesn’t change much as the battery is discharged, for example, NiCd and NiMH.
The voltage of others drops off as the battery is discharged, for example, zinc-carbon, and alkaline.

9. Check out the nominal voltages (3.6 V, 2 V, 1.5 V, 1.2 V).
Some voltages are flat (SLA, Ni-Cd, NiMH). Others drop off with discharge (Li-ion, alkaline). The drop off of Li-ion is somewhat misleading. It starts at a higher value, so it’s actually flatter than it looks.
Note how the alkaline battery voltage quickly drops off and becomes about the same as NiCd and NiMH (1.2 V). That’s why it’s usually OK to replace alkalines with NiCd and NiMH.

10. Discharge and Current
Battery capacity, usually expressed in mAh, is measured under specific conditions.
The higher the current, the less the effective capacity.
Example: A battery rated at 1500 mAh may be able to deliver 150 mA for 10 hours, but it may not be able to actually deliver 1500 mA for 1 hour.

11. Peukert Curve (from http://www.batteryuniversity.com/partone-16a.htm)
On the left, high current.
At high current, the effective capacity of a battery is greatly reduced.
At low current (on the right), battery meets capacity specifications.
Intermittent use can prolong battery life.
Note that at 1 C, the effective capacity is only 30% of the rated capacity. This is for a specific battery – every battery type will be different.
For example, a capacity of 2.8 A-h for a NiMH AA is measured over 5 hours, so that’s a current of .56 A for 5 hours, not 2.8 A for 1 hour.

12. C Rate Calculations C = Rated capacity/ 1 hour
Example: A 2800 mAh NiMH battery has a C of 2800 mA.
Batteries can be tested at various multiples of C.
Example: For the 2800 mAh battery, C/4 would be 700 mA; 3C would be 8400 mA.
Skip this slide.

13. Voltage Dependence on Current
Batteries are not ideal devices – They have internal resistance.
Vloss = IRinternal
Battery Type
Typical Internal Resistance (milliohms)
NiCd 1.2 V AA 30
NiMH 1.2 V AA
150
Li-ion 3.6 V
320
Alkaline 1.5 V AA
Example: If you draw 2 A from an NiMH battery, the voltage will drop .3 V – down 25% from its rated voltage.
The internal resistance depends on amount of discharge, the number of charge/discharge cycles the battery has been through, and the temperature. The 150 mOhm value for the alkaline AA is based on a measurement at 22 C. It has much higher resistance at lower temperatures.

14. Maximum and Suggested Drain
Battery Type
Max Drain
Suggested Drain
Alkaline
.5 C
< .2 C
SLA
.2-5 C
.2 C
NiCd
2-20 C
< .5 C
NiMH
.5-5 C
Li-ion
1-2 C
< 1 C
Skip this slide.
These numbers are only approximate.
Max value – Use it if you must, and only briefly.
Suggested drain – Use this for continuous applications.
Some batteries will have max discharge specs.

15. Batteries in Series Batteries should be identical.
Total voltage = Voltage of each cell x number of cells
When using rechargeable batteries in series, beware of deep discharge because of polarity reversal.
Polarity reversal is not usually a problem for 2 cells in series. The more cells you put in series (e.g. 6), the worse the problem gets.
Some appliances state: “Don’t mix battery types. Don’t mix old and new batteries.” This is probably to avoid polarity reversal.

16. Batteries in Parallel Batteries should be identical.
Total current = Current of each cell x number of cells
Usually a bad idea
Good batteries may discharge through bad battery.
Batteries, even of the same type, may have slightly different voltage or discharge characteristics.
But hybrid vehicles routinely use batteries in parallel.

17. Illumination Economics
Incandescent, Compact Fluorescent (CFL), and LED lighting characteristics
Type
Cost of bulb
Lumens
Efficiency
Lifetime
60 W Incandescent $1
840 2%
1K hours
(~ 1 Month)
13 W CFL $2
825 9%
10k hours
(~ 1 year)
10 W LED $6
810
12 %
50k hours
(~ 5 years)
This doesn’t really go with the stuff on batteries, but I couldn’t find a better place to put it.
These three bulbs compare well as to their light output. Note that CFLs and LEDs last much longer than incandescents.
Note the poor efficiency for incandescents. They waste 98% of the electrical energy as heat.
CFLs are also known as curlicue bulbs or Al Gore bulbs.
Note that Lifetime is the amount of time the bulb will last if you turn it on and leave it on.

18. Total Cost by Bulb Type
Cost for purchase of bulb(s) and for electrical 10 ₵/kWh.
But this assumes you turn the light on and never turn it off until it blows out and you replace it.
Type
1 month
1 year
5 years
60 W
Incandescent $5
$62
$307
13 W CFL $3
$13
$67
10 W LED $7
$15
$50
So this is the cost, considering how much you pay for the bulbs and how much you pay for the electricity to power them.
Note that the times are for bulb life, not for actual time. If you turn the light on only for 1 hour per day, an incandescent will last 2 years, a CFL will last 25 years, and an LED will last a century.
Furthermore, on/off cycling shortens the life of CFLs, and, to a lesser extent, incandescents.

19. What’s so Bad about CFLs?
On/off cycling shortens lifetime.
They are sensitive to physical shock and breakage.
Most CFLs are not dimmable.
Some people don’t like the quality of the light (too harsh).
Some CFLs take time (~ 30 seconds) to achieve maximum light output – not a problem for newer CFLs.
CFLs contain a small amount of mercury (a disposal issue).
Low temperature reduces CFL light output (an outdoor use issue).
High temperature shortens CFL lifetime (a luminaire issue).
Cycling reduces lifetime of incandescents, too, but not as much as CFLs. If you turn a CFL on/off every 5 minutes, it shortens lifespan to the same as an incandescent.
Conclusions:
CFLs are better than incandescents for most applications. You’ll save money with CFLs.
But incandescents and LEDs are better for high cycling locations or for short-time locations such as
* Garage door opener lights
* Closets
* Short-term motion sensors
* Refrigerators
LEDs are becoming much more affordable. Use them when you want to avoid some of the CFL problems.