Many typical battery cells used in RC systems and electric flight look almost the same physical size; it’s important to read labels. L-R: two typical Ni-Cd cells, NiMH cell, AA alkaline nonrechargeable battery cell, new Li-Poly cell.

My apologies. I had every intention this month of publishing my new Radio Control (RC) electric sailplane model that I hope beginners will build from scratch. (It's not a kit or an Almost Ready-to-Fly [ARF]/Ready-to-Fly [RTF] model!) As I learned, designing, building, flying, photographing, and writing about it takes more than four weeks. I promise to publish my "Scratch-One" design next month.

This month (the eighth installment I've written) will be devoted to the all-important battery basics. In the previous seven chapters I've referred to the RC-system batteries and the electric-motor batteries on many occasions. I will probably repeat some of those points to emphasize their importance.

The battery power to your RC system is like putting gas in your car; if you run out of gas, the car doesn't run. If your RC system runs out of electrical power, it doesn't work (fly)! During this presentation I will concentrate mostly on the RC-system batteries, but I will get into some aspects of the electric-motor batteries as they are used in electric-powered flight.  

Typical RC system battery packs and charger. On left is RC

transmitter with rear compartment cover removed, exposing

eight-cell Ni-Cd battery pack (yellow). In center is dual-output

battery charger normally supplied with RC system. On right are

two typical four-cell Ni-Cd airborne battery packs (the ones that

go in model).

Many of Bob’s battery packs for electric flight. There are too

many to keep on trickle charge at once, so he doesn’t!

Types of Batteries: In the RC hobby today, modelers typically use Nickel Cadmium (Ni-Cd) or Nickel Metal Hydride (NiMH) cells. Both are rechargeable batteries. Under normal operation they can be recharged hundreds of times and have been known to last an average of three to five years and more.

From a beginner's perspective Ni-Cd and NiMH cells provide roughly the same kind of service, so you need not worry at the start about what kind of cells were supplied with your particular RC system.

The NiMH cell is the newer of the two. It can offer more capacity than the Ni-Cd cell of the same physical size. More capacity means that it can operate your system longer or fly your airplane longer. NiMH cells have a slightly lower characteristic voltage under load than Ni-Cd cells. From an RC-system standpoint, that difference is of little concern because the load is relatively low.

However, when using NiMH cells for electric-powered flight, the difference can be important. If you fly a model with a seven-cell Ni-Cd pack, then substitute a pack with NiMH cells, you might have to go up one more cell to a total of eight to achieve comparable performance. With every passing day, advancements in NiMH battery technology are removing this deficiency.  

Some inexpensive (economy-type) RC systems are sold with no batteries included. If that is the case, you will have to purchase 12 AA-size alkaline (nonrechargeable) batteries (eight for the transmitter and four for the receiver or airborne side). Although these cells will last a long time (possibly 10 hours or more!), they must eventually be replaced since they can't be recharged.

Balsa Products sells a charger and eight individual NiMH cells which must be removed from the transmitter and placed in the charger. After charging is complete, the user inserts the cells back in the transmitter. The charger is $22.95 and a set of eight 1300 milliampere-hour (mAh) NiMH cells is $8.50. It's an interesting solution to what could become a costly long-term battery-replacement problem.

Balsa Products sells this eight-cell Ni-Cd or NiMH individual

battery-cell charger which comes with a set of 1300 mAh NiMH

cells, all for $22.95. You charge these cells by removing them

from RC transmitter.

There is a new type of battery technology called Lithium Polymer (Li-Poly), which has emerged thanks to the cellular-telephone industry. There isn't much application for this type of battery cell for RC systems at this time, but you will be hearing and reading more about the great advantages of low weight and high capacity for electric-powered flight. There will be more about that in another installment.  

Battery-Capacity Ratings: All batteries have a capacity or rating. The capacity can tell you how much power the battery can supply in a period of time, or how long the charge will last while powering your system, appliance, etc.