by Alan D. Tasker, WA1NYR

Since Military portable devices employ batteries, I thought it would be interesting to at least a few folks to see what insight we can gain from a review of battery technology over the past 60 or so years. This article is an attempt to put in one place a few facts about some of the more common types, most of which have been used by the military. Comments are welcome: atasker@ix.netcom.com

In a subject this complex, a divide and conquer approach is preferable. The first division is between Primary (use once, throw away) and Secondary (rechargeable). A second division can be made between "mainstream" and "specialty."

First, what are the relative advantages of Primary and Secondary?
Primary batteries offer the following two main advantages.

They have more energy density than secondary cells, so if long life between changes is a necessity, then this is the type to use.

The modern type (not those from the 40's and 50's) have low self discharge rates, so if the energy has to be there when you need it (flashlight for instance), use this type. Rechargables have a self-discharge rate of between 1%/week and as high as 5%/day.

Secondary batteries, on the other hand, offer the following two main advantages.

When you need sustained high current output, to start a motor for instance, secondary batteries are the way to go (but not all types are recommended for this service).

Life cycle costs are lower because of the ability to keep charging and reusing them.

Primary/Mainstream
Back in the 1940's, the "flashlight" battery (technically, a single is a "cell", multiple cells make a battery), otherwise known as the LeClanche cell (1.5V/) was the mainstream primary product. It didn't offer such a flat discharge curve, nor did it have a low self-discharge rate. Since that time, however, the Alkaline cell (also 1.5V/) has greatly improved things, and is the mainstream consumer product. After a flirtation with Magnesium cells (1.75V/), which offers excellent high temperature storage characteristics, the military moved on to Lithium Sulphur dioxide cells (3V/). Offering about the same capacity of present day alkalines (but more than the older alkalines), a super light weight, and a super low self- discharge rate, their potential for releasing poisonous gas will most likely be their downfall. They are capable of outputting high currents, but cell heating is of great concern because of the possibility of cell rupture.

The new kid on the mainstream block is the Lithium Manganese Dioxide (3V/) chemistry, offering a 25% to 50% increase in capacity over the Lithium Sulphur Dioxide cell, and low toxicity. Both of these Lithium chemistries offer superior low temperature operation, and very light weight. Capacity testing, however, is problematical. There is another type of cell just now appearing, the LiFeS2 (1.5V/). Maybe this is a lithium chemistry that can replace the so-called "flashlight" cells, i.e. alkalines?

Primary/Specialty
Back in the 40's again, the Mercury battery (1.35V/) was a specialty cell, offering long (2-3 years) of shelf life. It was the chemistry of choice for many years, especially in the rescue radio field. It was only replaced in the relatively recent PRC-112 with LiSO2. But environmental concerns plus better chemistry offers more today. Even the LiSO2 is being replaced, as noted above, with the LiMnO2.

For completeness, we should mention water-activated batteries (magnesium/silver chloride for example) as used in sonobuoys and such. Also, thermal battery types as used in missiles.

More on the commercial side, there are also a host of specialty cells for watches, hearing aids, etc., such as silver oxide, zinc air, etc.

Secondary/Mainstream
Back to the WWII period again, we find the Lead-Acid cell (2v/) as the chemistry of the moment. It has remained in its place as the leading motor start battery, and it is hard to beat. The lead-acid cell works best when it is kept charged in what is called a "float" application, as in vehicles or in emergency lighting applications. Although there are deep discharge types available, immediate charging is necessary in order to prevent sulphation, which destroys the cell. There are battery charging/reconditioning products on the market that claim to rejuvenate sulphated cells. I have no first hand knowledge about the veracity of these claims.

The lead in the lead-acid cell is too soft for use as is, so it needs a small percentage of a stiffening agent to be mixed in. Antimony was chosen in the beginning. This chemistry caused a fair amount of water loss, so a sealed construction (so called SLA, sealed lead-acid) was not possible. In recent times, Calcium amongst other materials has been used in place of Antimony, leading to less water loss. This type of battery is available in both sealed and vented construction. The so-called Lead-Calcium battery is in reality a lead-acid type with Calcium as a stiffener. It was the chemistry of choice for “stationary batteries” as used in fixed installations like Telco CO (central office) and microwave relay applications. Installations seem to be going in the SLA direction of late.

Perhaps it was the aircraft industry that fostered a lighter replacement, and thus enters the Ni-Cad cell (1.25V/). Unlike the lead-acid, these can be completely discharged, and in fact, can give better service this way. There are two types of plates used. Most of the non-sealed cells did not use sintered plate construction. The sealed type does use sintered plate construction, which yields a higher capacity cell. However, when the sintered plate types are used in float applications, they tend to remember this light usage, and do not deliver their full rated capacity (so called memory effect). Even the airline industry is tiring of the NiCad problems, and is looking at either lead acid or some form of Lithium Ion.

The above two chemistries offer the highest amps-in-a hurry of anything available, both in discharging and in recharging. The following two types are not so robust in these areas, at least today.

The Nickel Metal Hydride (1.25V/) (is rumored to have the memory effect too, but it may just be a settling out kind of thing) and the Lithium Ion (1.5-3.9V/ depending on exact chemistry) have about the same energy density and were developed at about the same time. It appears that the early leading but somewhat problematical NiMH will give way to the Lithium Ion.

Secondary/Specialty
The Edison cell (1.2V/) has just one overriding feature; you just about cannot kill them. Railroads used them for years, just changing the electrodes and/or electrolyte. Did the phone company use them in their CO?

The silver cell (1.5V/) has been used by both the Soviet and the US military. They offer tremendous capacity at a fairly light weight. The downside: They do not take many charge/discharge cycles (dendrite growth causing plate-to-plate shorts). Thus, there is not much life over which to amortize the high cost. The Soviets added some Lithium Hydroxide to each cell, perhaps leading to a longer life???

In Space work, there is the rechargeable Nickel Hydrogen chemistry. Each cell must be fitted with a "bypass module" (contains diodes) so as to allow the battery to continue to operate (both charging and discharging) in the face of an open cell.

Lastly, there is the battery with "super cap" included. The capacitor supplies the amps-in-a hurry, so that any suitable battery chemistry can be used. Products are beginning to appear on the market.

With sincere thanks to Brooke Clarke for his helpful comments.

More information on Primary chemistries can be found at…… http://electrochem.cwru.edu/ed/encycl/art-b02-batt-nonr.htm http://www.powerstream.com/BatteryFAQ.html#AlAir

More information on Secondary chemistries can be found at…. http://www.powerstream.com/Compare.htm

Information on battery charging can be found at….
http://www.powerstream.com/tech.html