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Batteries

There are three important decisions to make when you take the plunge to fly electric.

Airframe. Will be based on how you want to fly and personal preference.

Motor. Must be appropriate for the airframe you choose to maintain the flight envelope you enjoy.

Battery Pack. Will determine motor performance and flight durations.

There are three factors that must be considered when choosing a battery. The type of airframe you choose and your style of flying will play a part in your decision.

First you must consider weight. A heavier pack in a large wing slow flyer might be acceptable while the same pack in a scale warbird may make the plane (because of wing loading) tough to fly especially at slower speeds.


A second consideration will be how long you wish to fly. The mah (milliamperes per hour)rating of a pack will be almost directly proportional to the length of time you wish to fly. If you have a 600mah pack in airframe X and can fly for 6 minutes, switching to a 1200mah pack of the same voltage should give you about 12 minutes. This is close enough for our discussion but technically the added weight of a larger pack will shave a little off your flight time.

The third factor is cost. As weight goes down in battery technology, price goes up. And of course as amp hour ratings go up, so goes cost (and weight).

Lets compare the three major battery types popular in todays E-planes.

The most popular are Ni-Cads (Nickel Cadmium). Availability, ease of charge and maintenance, ruggedness and low price are a few reasons for their popularity. But (there is always a but) Ni-Cads are the heaviest.

Next, and gaining popularity very fast are NiMH (Nickel Metal Hydride). They are a little pricier than there Ni-Cad counterparts, but are somewhat lighter per mah. So, for a given weight, you can get longer flight durations. Most chargers designed for Ni-Cads can also handle NiMH.

The third technology is Lithium-Polymer referred to here as LiPo's. First and foremost LiPos's can be dangerous. More so that the two aformentioned types. If overcharged or shorted a single LiPo cell can explode and or catch fire.
By fire, I mean a blow torch, not just a puff of smoke. These batteries must be handled, charged, discharged, and maintained with great care. OK,that said, this is the lightest of the three. You can really get a lot of juice for the weight.

Note. By definition a battery is a group of cells. A single Ni-Cad or Ni-MH cell will generate 1.2 volts (force). Hence, when you hear reference to a 7 cell pack just multiply 1.2 x 7 to get the pack voltage.
How long it will supply that force is measured in milliamp hours (capacity). As an example, a 1200 mah pack will supply 1200 milliamps (1.2 amps) of current for 1 hour before you will have to recharge.

A single LiPo cell will generate 3.7 volts. Packs will typically be 7.4v (2 cells) or 11.1v (3 cells)

Here are some comparisons.

 
7 cell 8.4v 730mah NiMH. weighs in at 3.4 oz. and cost around $30.   8 cell, 9.6v, 950mah NiMH weighs 6.3oz. and cost ~$20.00
     
 
2 cell 7.4v, 1200mah Lipo. 1.9 oz and cost $35.00  

3 cell11.1 v, 1200mah Lipo. 2.8oz and cost
~$52.00

As you can see, LiPo's offer a lot of go juice at the least weight. They cost significantly more
than other types and require a special charger. More on chargers on the charger page.
NiCad is a reliable, safe, affordable technology and will be with us a long time.

Did I mention LiPo's can be dangerous?