Testing Rechargeable Alkaline Batteriesand More

So, do those rechargeable alkaline batteries work? The ARRL Lab investigates.

By Ed Hare, KA1CV, and Mike Gruber, WA1SVF

When we were first asked if the ARRL Lab could produce an article on rechargeable alkaline batteries, it looked so easy. We had previous testing experience with portable gel cells and lead-acid batteries and assumed the rechargeable alkaline products would follow nicely. For the most part, that turned out to be so. There were however, enough surprises, interesting results, and no small number of side roads in this project to provide good fodder for a QEX article. For a while it looked like the project was taking on the life of the Battery Bunny. (Or perhaps the cat with nine lives. Do you remember that frisky feline from late 50s TV commercial fame or are we dating ourselves a bit?) Here at last is the entire saga of the ARRL Lab's battery testing that kept going, and going, and...

While we initially concentrated on the rechargeable al-

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kaline batteries, we also took a brief look at some other battery types, primarily to verify some of our conclusions about the alkaline batteries. We'll summarize these batteries near the end of this article.

April 1996 3

Rechargeable Alkaline Batteries

The only rechargeable alkaline batteries currently available are the "Renewal" brand manufactured by Rayovac. We obtained an application note and data sheet from Rayovac. A summary of the data from the application note is shown is shown in Table 1. (The application note states clearly that the data are not specifications.) These are 1.5-V batteries that can be used "25 times or more," according to the application note. The manufacturer was kind enough to include a press-release kit containing all sorts of marketing information and photos. This material did educate us a bit about "rechargeable alkaline-manganese" (RAM) batteries. A current application note or other information on Renewal cells can be obtained by calling Rayovac's Renewal help line at 1-800-237-7000.

In outward appearance, these rechargeable cells look remarkably similar to ordinary alkaline batteries. Ac cording to the application note, these batteries have been around laboratories for over forty years. Previously, however, they suffered from a number of problems, including internal pressure generated by hydrogen gas, internal shorting due to dendrites, nonreversible chemical reactions from excessive discharging and separation of internal cell components. Rayovac purchased the rights to a patent held by a Canadian company to overcome these difficulties and made further improvements. The outcome of Rayovac's hard work included a "new unique patented formulation," the necessary charging system and an expanded product line of four cell sizes. The resulting Renewal cells, introduced in 1993, became the first rechargeable alkaline batteries to become available on the commercial market.

The Charging System

After educating ourselves about the alkaline batteries in the application note, we looked into the charging system: the "Power Station," as Rayovac chooses to call it. We purchased an eight-cell model for $45.00 from Newark Electronics.1 (They are also available in many department stores.) In outward appearance, the Power Station looks much like any other charger. The one we obtained can simultaneously charge up to eight cells, but a Power Station for up to four AA or AAA cells is also available. Much to our dismay, neither the manual nor application note included circuit details on the charger. The only technical tidbit of significance in the manual describes the use of a "microchip" to monitor each battery while being charged. We did, however, note that Renewal cells must only be charged in the Power Station, so we suspected it must be something a bit out of the ordinary. The manual contains a stern warning not to charge standard alkaline batteries. In fact, the mechanical design of the charger is such that standard alkaline batteries will not make contact with its charging posts.

This is not enough information for us technoid types, so we turned to an oscilloscope in hopes it would reveal just what magic the charger generates. We discovered the waveform changes significantly over the charg-

1 Newark Electronics, 4801 N. Ravenswood Avenue, Chicago, IL 60640-4496. Tel: 312-784-5100.

Table 1—Typical Data for Rayovac "Renewal" Brand Rechargeable Batteries (Original Formulation)

Specification

Dcell

C cell

AA cell

AAA cell

Nominal Voltage

0 0

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