Amperage is the thing.

The condition of your battery and how well it accepts a charge can mean everything in a race. It affects available "punch" and run-time and is the foundation for everything that operates an electric-powered vehicle. This article provides a good working knowledge of batteries that will help you finish races and get the longest life out of your packs.

The Battery Pack

Most electric R/C vehicles use a rechargeable nicad (nickel cadmium) or nimH (nickel metal-hydride) battery pack made of six 1.2 volt sub-C* cells connected in series to produce around 7.2 volts ranging from 1.5 to 3 amps (1500 to 3000 mah.)** If the leads are shorted against metal, the resulting amperage can exceed several hundred amps, leaving a weld-mark. Always exercise caution when charging or handling R/C battery packs - they have the potential to explode and can cause serious injury!

Battery packs come in a wide range of configurations from hundreds of manufacturers, as do their chargers. You can buy pre-made packs or individual cells and assemble the packs yourself. A few important highlights:

• Nicad (nickel-cadmium:) For many years, nimH batteries have been the battery type of choice, but many racers still use and prefer nicads. Nicads require complete discharge after use. If not completely discharged, the pack will form a "memory-" that is, the still-charged area of the cells won't accept charge any more, and the pack will lose it's punch and have a shorter run-time. If you want your nicads to last, buy or build a good discharger when you buy your batteries and charger, or build one on your own from standard auto bulbs like the "Christmas tree" discharger shown at the right. Running the RC until the wheels stop turning is not sufficient discharging - the amperage draw is not heavy enough to draw out all of the electricity in the pack.
• nimH (nickel metal-hydride) More environmentally friendly and not requiring the rigorous maintenance of nicads, nimH are quicky becoming the standard pack for the electric racer. Unlike nicads, you do not want to discharge nimH batteries down to almost nothing; this will shorten their life. NimH batteries should only be discharged to approximately 30% capacity and can be safely stored in this condition. You also need a charger that is specifically designed to charge nimH batteries - a nicad charger can damage nimH batteries.
• Stick or side-by-side: A "stick pack" is the most common assembly configuration, with three cells end-to-end in two rows. In a side-by-side pack all six cells are laid side-by-side, with the battery ends exposed. This is the best configuration for the "elite" racer as it allows access to the positive and negative ends of each individual cell. When discharging, this allows you to discharge the cells individually as opposed to discharging through the main connector, providing the most even discharge of the cells. If you can discharge them evenly, they will charge evenly. This will provide a more "punchy" charge and the pack will last much longer.
• Matched and unmatched packs/cells: When buying a battery pack, try to buy a "matched pack." A matched pack or set of cells is one that all the cells have been conditioned, tested, and labeled by the manufacturer and all the cells in the pack have the same or very close to the same average voltage. This means that all the cells will charge and discharge evenly, providing the longest run time possible. If properly charged and maintained, a matched pack will have a longer life than an unmatched pack and will provide a consistent charge from run to run. This author highly recommends the information provided by Pro-Match Racing on their What the Battery Numbers Really Mean page.
• Chargers: Be sure the charger you buy is compatible with the type of packs you buy. "Back in the day" any charger would do, because you would manually "peak" the nicad pack's charge using a voltmeter to detect peak detection. Today's chargers "auto-peak" and have specific settings for charging rate and type of battery. Again, it is important not to charge nimH packs on a nicad charger. Use only a charger that is designed for nimH charging or you will damage your expensive battery.

The battery configuration is one of the many options you can customize to provide more power to your R/C. With a speed control that can handle the voltage, running a pack with more than six cells will increase peak RPM of an electric motor drastically. Electric powered dragsters generally run a 20 cell pack, providing a whopping 24 volts!

About Connectors
One of the points at which electrical current can be lost is at the various connectors that carry the power from the battery, through the ESC, and to the motor. Most R/C batteries and other equipment come with what is known as a "Tamiya" type connector. The Tamiya connectors are made of potmetal and are loose fitting and highly inefficient, building resistance at the connection point. It's not uncommon after a run to find the connectors themselves hot or even close to melting.

One of the first things you should do when fitting a battery or any other main electrical component on an electric R/C is remove the Tamiya type connectors and replace them with one of the many low-resistance connectors available on the market. It's a good idea to settle in on which type of low-resistance connector you're going to use and stick with it so that as you buy more batteries, a different ESC, or a motor, you'll have your system "standardized" with the same type of connector everywhere.