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Battery Selection
All wireless microphone transmitters (and some receivers) rely upon batteries for their power. Selecting the correct type of battery will help ensure reliable wireless performance and satisfactory battery life. There are a number of basic types of batteries available. Of these, five types are capable of powering Audio-Technica wireless equipment: alkaline, zinc-carbon, lithium, rechargeable nickel-cadmium and rechargeable nickel metal hydride, with alkaline being the preferred choice.

The five types of batteries differ widely in their useful life, with zinc-carbon and nickel-cadmium ("ni-cad") batteries having the shortest life and lithium batteries the longest. Typical battery life can range from an hour or so for the zinc-carbon battery to 25 hours or more for a lithium battery. Alkaline, zinc-carbon and lithium batteries can only be used once, while the nickel-cadmium and nickel metal hydride batteries can be recharged and used many times.

Zinc-carbon batteries are not recommended for wireless transmitters except in an emergency. Only better quality zinc-carbon batteries from well-known companies should even be considered. Cheaply made "toy" batteries sometimes last only a few minutes because of poor construction and low storage capacity. This type of battery also starts losing capacity as soon as it is made, and packaged units in local stores might have already lost more than 50% of their original capacity. Zinc-carbon batteries perform poorly when cold and, at best, have only about 25% to 35% of the useful life of an alkaline battery. Perhaps worst of all, they often leak badly and can completely ruin a transmitter in only a few weeks if not removed.

Audio-Technica does not recommend the use of rechargeable ni-cad batteries. Readily available "9-volt" ni-cad batteries are usually really only 7.2 volts when fully charged and have only 15% to 20% of the capacity of good alkaline batteries. The lower voltage will result in significantly reduced transmitter power within a short period of time.

Premium "7-cell" ni-cad batteries are available, but may be difficult to find. These units have approximately 25% of the capacity of an alkaline battery, and tend to be very costly. Another serious problem is that ni-cads exhibit a "memory effect," such that their capacity declines rapidly if they are not fully discharged each time they are used. This can be a particular problem with wireless equipment, since the fully discharged voltage is below that required for satisfactory operation of the transmitter.

Nickel metal hydride (also called NiMH or NH) batteries are a more acceptable choice for a rechargeable battery. Premium models are true 9-volt designs and have about 60-70% greater capacity than most premium ni-cad batteries. The most important advantage of nickel metal hydride batteries, however, is that they are essentially free of the "memory effect" that is so troublesome in ni-cad batteries. Unfortunately, these advantages come at a price; premium NiMH batteries generally very costly.

There are two other potential problems with using either ni-cad or NiMH batteries in wireless transmitters. One is that even "discharged" batteries will work acceptably for a minute or two, and it is very easy to mix up charged and discharged batteries. In addition, it is very easy to forget to charge the batteries after each use. These problems often result in embarrassing transmitter failures.

Lithium batteries provide approximately three times the life of an alkaline at six to eight times the cost. There are a few situations where the extra life is worth the added cost, but the operating life provided by alkaline batteries is more than adequate for most purposes. The low temperature performance of lithium batteries is also considerably better than for alkaline batteries, an advantage in certain situations. For economy, Audio-Technica recommends using lithium batteries only in special situations where the extra time between battery changes is necessary or where use at very low temperatures is required.

Alkaline batteries are the preferred choice for powering wireless transmitters. They are convenient, offer an excellent balance between cost and operating life, and are reliable. In addition, they are widely available, hold their capacity well in storage and usually do not begin to leak for several years. The market for alkaline batteries is also quite large, and competition is likely to keep prices low.

Battery Life
Sometimes it appears that batteries are providing less than the expected operating life. When this happens there is a tendency to blame the wireless transmitter for the apparent problem. However, only very rarely does a transmitter's power consumption actually increase. The vast majority of transmitter failures result in less power being drawn from the battery, not more. While a sudden jump in transmitter power drain is not completely unknown, in most cases the actual problem is related to the batteries themselves.

There are several reasons why battery life may appear to be short. Because used batteries don't look different from new ones, it is very easy to mix used or partially used batteries with brand new ones. Often, partially used batteries are kept for other purposes, such as for use in small electronic devices or toys. To avoid problems, it is suggested that batteries removed from wireless transmitters be immediately set aside for recycling or discarded if they are of no further use.

If used batteries are to be kept for another purpose, they should immediately be permanently marked to indicate that they are not new and placed in a separate location. An inexpensive battery tester is a worthwhile investment, both to verify that new batteries are really new and to estimate the remaining life of used batteries. Careful handling of batteries is absolutely essential to trouble-free wireless operation. On any particular occasion, the difference between success and failure with wireless can be as simple as mixing up the old battery and the new battery during a change.

Sometimes wireless users forget to turn off wireless transmitters when they are not actively being used. When use resumes after a delay or break, the battery life may appear short because the idle time is not being considered. The drain on a wireless battery is essentially the same whether or not audio is being transmitted. Similarly, if a transmitter is only used an hour or so per day or per week, it is very easy to lose track of the total operating time on the battery.

Batteries that are purchased as new might not have the expected operating life if they have been in storage a long time, or have been stored in a hot, humid location. Even when batteries are date coded, it is possible that a significant percentage of their capacity has been lost well before the expiration date. The expiration date is based upon some percentage of the original capacity, such as 75%. If the batteries have been stored for one or two summers in a warehouse without air conditioning, the actual remaining capacity could be less than 50% of original. High humidity also shortens battery life significantly.

If, after the above considerations, you believe that new, fresh alkaline batteries are providing less than the expected operating life, please contact Audio-Technica or your dealer for further assistance.

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