By William Laxson, MRA Communications Committee Chair
Over the past 40 years, the chemistry used inside our rechargeable two-way radio batteries has undergone several major evolutions. In the 1970’s, nickle-cadmium batteries (NiCd) were widely used.
Then about 20 years ago, the industry began a shift to nickle-metalhydride (NiHM) batteries to reduce environmental pollution by the cadmium (a heavy toxic metal) waste stream.
More recently manufacturers have been transitioning to lithium-ion (LION) batteries because of their higher energy density and the desire to reduce the size and weight of the battery in concert with the size and weight reduction of the associated radio that can be achieved with modern microelectronic circuitry.
Each battery chemistry has its own unique set of operational characteristics that the end user should keep in mind.
We desire many characteristics in our batteries, including low cost, high energy density, and light weight.
Battery characteristics should not change at low and high temperatures. They should have no memory effect, offer a large numbers of recharge cycles, and leave no hazardous heavy metal waste disposal issues when the battery reaches the end of its life.
No battery chemistry yet developed can be optimized to maximize all of the favorable characteristics at the same time. Battery
manufacturers tweak whatever chemistry they are using to emphasize some characteristic over others based on how the battery is expected to be used.
The characteristics most important to the SAR community (because they have a direct impact on the actual use of the radio in the field) are battery life and reliable operation over a wide temperature range (that extends down well below zero for many teams operating in northern climes or at high altitudes).
All other undesirable characteristics can be managed with varying degrees of inconvenience and cost because the radios are not in field service.
There are three major battery chemistries in use today in our rechargeable two-way radio batteries, NiCd, NiMH, and LION.
may be available from aftermarket manufacturers like Alexander or TEI4. NiCd is the most robust battery technology of the three in use today.
NiCd Advantages:
They are very tolerant to widely varying charge and discharge conditions (and temperature), even after long storage periods
in a discharged state.
They provide the highest number of charge/discharge cycles when properly maintained (1000 or more), hence lowest cost/
cycle.
They have the longest shelf life in any state-of-charge (important because of higher self-discharge rates).
They have the best low temperature performance, maintaining 60% of capacity at minus 20oC (4oF).
NiCd Disadvantages:
They have a lower energy density when compared against newer battery chemistries.
They exhibit the strongest memory effect. They must periodically (monthly) be exercised to a full state of discharge.
NiCd is environmentally unfriendly, containing the toxic metal cadmium.
They have a modest self-discharge characteristic, losing 10% of their charge in the first 24 hours, then continuing at a 10% per month rate thereafter.
NiMH: Nickle metal hydride batteries can be found for most models of modern two-way radios.
NiMH Advantages:
They have a 50% percent higher capacity over a standard NiCd, with potential for greater improvements.
They are less prone to memory effects than the NiCd batteries.
Periodic exercise cycles are required less often, but are still critical to maintaining a long battery life.
They are environmentally friendly and profitable to recycle.
NiMH Disadvantages:
NiMH battery service life is more limited compared to NiCd, particularly when deep cycled at high load currents (i.e. twoway radio transmit mode to battery end-of-charge). Shallow rather than deep discharge cycles are preferred. Expect 300 discharge cycles and 300% the cycle cost of NiCd.
They are less tolerant to charge conditions. The battery generates more heat and takes longer to recharge.
They have a 50% higher self discharge rate than NiCd batteries.
They have a poor shelf life when stored at elevated temperatures. They should be stored in a cool place and at a state-of-charge of about 40 percent.
NiMH batteries have poor low temperature capacity retention. At minus 20oC (4oF), expect to get only 20% of the room
temperature capacity. If the battery is warmed up, some capacity will be returned.
ION: Lithium ion batteries represent the most recent development in rechargeable battery technology. They have significant low temperature operation and cycle cost disadvantages in the SAR environment.
LION Advantages:
They have the highest energy density, primarily because of their high 3.7 volt per cell open circuit voltage.
They have no memory effect, and only half the self-discharge rate of NiCd batteries.
LION Disadvantages:
They are extremely sensitive to charging conditions. To extend cycle life and avoid damaging the battery, most LION cells are
operated by cycling them between the 80% and 20% capacity points.
Battery overcharge, over-discharge, or physical damage can induce thermal runaway, leading to flames and explosions.
Most high capacity LION batteries suffer from age related degradation of the cathodes, leading to a 20% reduction in capacity per year, whether the battery is in use or not.
LION batteries have extremely poor low temperature capacity retention. At minus 20oC (4o F) they stop working. If the battery is warmed up, some capacity will be returned.
