Batteries are both the achilles heel of electric vehicles, and essential for their operation. It is with batteries that the electrons are stored that make the vehicle move. Roughly speaking, the number of electrons you can store in the vehicle determines how far it will go. The angst of batteries in electric vehicles is the speed and range characteristics you can get in the vehicle using the battery technology available. The common battery technology, lead-acid batteries, have been in use for nearly 200 years and have changed relatively little in that time. By contrast think of the changes and improvements the internal combustion engine has seen in that time. In the late 1800's, in the infancy of the automobile, internal combustion engines were so unreliable that the most popular cars were electric, due to their ultra reliability. How times change, eh?

The typical batteries used by hobbyist EV conversions are lead-acid based, and generally offer 60 mile range at highway speed. While this is greater than most peoples daily driving needs, it is a lot less range than we enjoy with gas-cars. It helps to understand the electrical basics that control range so that we can make better choice.

How do we measure the range capability of a battery pack? The electrical measurement of interest is "kilowatt-hours" (see electrical basics for a more complete discussion).

1 kilowatt-hour = 1 kilowatt used over 1 hour

1 kilowatt = 1,000 watts

To bring this to every day terms, the typical lightbulb is 100 watts, yes? If you have ten 100 watt lightbulbs, that is 1,000 watts. Leave them running for an hour, and that is a kilowatt-hour. By modern electricity rates it will cost you in the neighborhood of ten cents for that electricity.

What determines the range capability of a given vehicle with a given battery pack is the power density which in turn determines the amount of kilowatt-hours of electricity that can be stored in the vehicle. As an electric vehicle moves down the road, it consumes electricity through the power controller and motor. Say the vehicle has a 120 volt electrical system, and uses 30 amps to cruise, therefore the vehicle cruises at 3.6 kilowatts. If the vehicle is run for an hour, it consumes 3.6 kilowatt hours of electricity.

These two measurements concern the carrying capacity of the vehicle:

volume = the size of the area for batteries
weight = the carrying capacity of the vehicle

The vehicle can carry only so much weight and volume before it is overloaded. One tradeoff you might run into is whether to sacrifice the back seat of the car to carry more batteries (and hence have more range), but that would make the car less useful because it would no longer has a back seat.

Battery "power density" is measured these two ways

volume power density = kilowatt-hours / liter
weight power density = kilowatt-hours / kilogram

Tieing these two measurements together, your vehicle has a given volume and weight in which it can carry batteries, and depending on the power density of the batteries you will end up with a given kilowatt-hours of capacity.

Now we can begin to understand the achilles heel aspect of batteries. Namely, they have a poor power density versus gasoline. To demonstrate, let's compare batteries to gasoline, ignoring the physics teacher in the corner scolding us for comparing apples and oranges. First, let's assume we're using a regular 4-door sedan sort of car. If it were an electric car, the batteries (assuming lead-acid) to move it 30 miles weigh in the neighborhood of 500+ pounds. If it were a gasoline car 30 miles requires 1 gallon of gasoline, and is easily carried around in the ubiquitous "gas can". If you run out of electricity, can you easily carry that 500+ pound battery pack to the electricity station and get a recharge? Nope, not even if there were electricity stations.

The target range/speed

I believe there is a target speed and range capacity the car makers have in mind before they will support electric vehicles, which is 300 miles at "highway speed" (70-80 miles/hour) in a 4-door sedan that has a full trunk area available to the passengers. That target would be a direct replacement for current cars, because that's the range and speed we get today with gasoline.

Instead of seeing that range and speed, we get a lot less. With lead-acid batteries, the typical 4-door sedan as an electric vehicle gets 50 miles range at highway speed. GM's EV1 got 70+ miles of range on lead-acid batteries, and had a very aerodynamically clean design. Of course the car makers also have another problem with electrics, in that they have a duopoly relationship with the oil companies and these two camps are so in bed with each other that they can't see their way towards offering an alternative. But then that's a story for a different article.

Nickel-Metal-Hydride (NiMH) batteries get around twice the power density of lead-acid, and GM's EV-1 when powered with NiMH got 140 mile range. Lithium batteries get around four times the power density. Some experimental EV's powered by Li-ION batteries have been built, and get a 300 mile range at highway speed. This puts us near the desired speed and range capacity. Both of these battery types are very expensive, and are not being produced as large-size batteries of the type you'd expect in a full size car.

The other side of the battery problem is the time required to charge the batteries, generally taking many hours. For certain battery types or charging algorithms you may have a faster charging time, and in some instances it can be instantaneous charging. Generally speaking batteries don't like to be charged that fast and it hurts their life, reducing the number of cycles they can get. But some specific battery designs are able to take high charging rates without problem.

Describe and cover what charging rate means

Describe cycle life

Describe the power density measurements

Describe various battery chemistries, and general ranges of critical measurements

Batteries in a Portable World (http://www.buchmann.ca/default.asp) A handbook on rechargable batteries for non-engineers.

Building your own NiMH battery pack:

http://www.rccentral.com/guides.asp?ATCL_ID=51&PAGE_NUM=146

http://www.rccaraction.com/rc/articles/build_battery.asp

On the other hand: Soldering directly to cells is bad, bad, bad. http://www.rcbatteryclinic.com/soldering.html

At the very least one should be careful to do the soldering quickly and efficiently to avoid heating the cell.

These people sell NiMH batteries with solder tabs already set up.

http://www.panasonic.com/industrial/battery/oem/chem/nicmet/index.html

Battery manufacturers A-Z: http://www.solarnavigator.net/batteries/battery_manufacturers_a_b.htm

http://www.sionpower.com/ - Developer of Lithium-Sulfur batteries that have even higher power density than Li-Ion or Li-Poly.

http://www.polyplus.com/ - Another developer of Li-S batteries.

http://www.kokamusa.com/ - The U.S. arm of a Li-POLY maker

Zinc-Air: http://www.electric-fuel.com/evtech/index.shtml

http://www.arotech.com/index.html

http://www.lbl.gov/Tech-Transfer/techs/lbnl0977.html

http://www.findarticles.com/p/articles/mi_m3165/is_n7_v27/ai_11010213

http://micro.magnet.fsu.edu/electromag/electricity/batteries/metalair.html

http://ecl.web.psi.ch/znair/

http://www.renata.com/content/hearingaid/quickguide.php

http://www.fta.dot.gov/2422_7246_ENG_HTML.htm

http://www.konarkatech.com/news_and_events/konarka_articles/2004/5_may/military_aerospace/portable_power_support.php

http://www.thehawaiichannel.com/news/1671849/detail.html - recounts the recall of the Lithium batteries in EV Global bicycles. They were able to get hot, and sometimes catch fire.