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Testing: You know what capacity is and how to charge a battery; now you must learn how to monitor or test your batteries to determine when they are running out of power and when they must be replaced. Just because a battery is only a year old, you can't assume that it has to be good and not worry about it. Some batteries die after only a few months of service!

There are two places where you will want to test batteries: at home (in your shop!) and at the flying field. Generally the at-home testing is necessary on a regular basis to determine whether or not your battery continues to provide power at or close to its rated capacity. At the flying field you want to know when it is time to stop flying because you are running out of power. At that point your options are to go home, fast charge the battery, or swap with a freshly charged battery.

For at home there are probably close to a dozen popular battery discharge testers on the market. I use the FMA Direct Einstein XL, which costs slightly less than $100 with the power supply. This device might soon be out of production, but that decision was not final as I wrote this article.

However, I wouldn't want to disappoint readers by describing a product that is no longer available, so I'll use the Einstein for this discussion. At the end of this segment I will supply the names and sources for several other testing devices I know are still on the market.

The Einstein is convenient because it has two separate outputs, making it possible to charge and/or discharge test, or even trickle charge, two different battery packs. The basic idea is to be able to charge/test a transmitter and receiver battery, and at the same time keep the two totally separate. Many of these battery-testing devices have two separate outputs.  

The Einstein is especially nice because it allows you to select discrete charging currents of 25-, 50-, 80-, 120-, and 140 mA. It also lets you select battery packs consisting of anything from two cells up to a total of 12. This applies to Ni-Cd and NiMH.

Another of the Einstein's features is the ability to overnight-charge battery packs up to 140 mA and 12 cells, then after a fixed 16-hour period have the charge level revert to a trickle. This can be accomplished without ever evoking the discharge test mode.

The basic use of any discharge battery tester begins by fully charging the battery at the overnight rate. If you're using the Einstein the next day, press the "Cycle Start" button, and a fixed 300 mA load will be placed on the battery. An LCD screen will begin to register your battery's capacity, expressed in mAh.

When a minimum voltage of 1.0 volt per cell is reached, the Einstein stops the discharge load and begins to recharge the battery at the rate you previously selected. The last mAh reading on the LCD screen is saved until you disconnect the battery from the output cable. Charging will continue for a timed 16-hour period, after which the battery will revert to a fixed 12 mA (nonadjustable) trickle-charge level.  

The rest of this story depends on how you interpret the mAh reading. I generally discard a battery when the capacity drops 20% from its normal rated value. If I have a 600 mAh-rated pack, I will continue to use it until it gets down to 480 mAh (600 less 20%).

Keep a logbook containing capacity measurements made on each identified battery pack during a period of time. You'll usually observe that a pack will provide close to its rated capacity for two or three years, then all of a sudden the capacity will begin to drop off.

Although I normally test-cycle my batteries only every three months or so, the minute I see the capacity start to drop I'll check it at least once a month. My experience is that a pack showing this characteristic will usually "go south" in a hurry. When it does, I discard the entire pack; I never "perform surgery" after locating the bad cell. It isn't worth it, and it can waste a great deal of time.

When discarding any battery pack, don't just put it in your garbage. Follow the manufacturer's recommendations and return it to a certified disposal organization (that goes for any type of battery cell).  

Besides FMA Direct, there are several other sources of battery discharge testing devices that I recommend. Tower Hobbies and Great Planes Hobby Distributors sell the Hobbico Accu-Cycle. You can learn more about this unit at www.hobbico.com/chargers/hcap0260.html, and you can download its operating manual there too.

One of the nice things about the Accu-Cycle is that it has two separate monitoring meters—one for each output—so you don't have to keep remembering to switch the meter from output to output. The price is roughly $80, which is reasonable.

Horizon Hobby Inc. sells the Hangar 9 Sure Cycle Battery Cycler (tester). You can find information about it at http://horizon.hobbyshopnow.com/products/description.asp?prod=HAN9525. The Hangar 9 unit does the same job of battery discharge testing. It has a single output meter, as does the Einstein. At $60, it is a bargain.

I wish everything in this hobby was perfect and easy, but it is not. One major problem with battery testing is that almost all RC transmitters manufactured in the Far East come with a diode placed in the charging-jack circuit. It is done to prevent the main power source from accidentally shorting, but at the same time the diode essentially blocks your access to the battery pack. This means that when you hook up the transmitter, via an adapter cable, to any battery tester, you will not be able to discharge it.

To correct this problem, some clever modelers have gone inside the transmitter and shorted out the diode. In the process of doing this, they could cause problems to other circuits and they are canceling the factory warranty.  

I prefer to simply remove the battery pack. Most transmitter battery packs can be accessed easily by removing a hatch cover, and the battery is usually attached with a connector. The trick is to unplug and remove the battery, then obtain an adapter cable that will allow you to connect the battery pack directly to the tester. The RC manufacturers usually sell these adapters, so try them first.