Comparison of NiCd, NiMH, and Li-Ion Batteries

Land mobile portables have traditionally used Nickel Cadmium (NiCd) and Nickel Metal Hydride (NiMH) batteries. Lithium-Ion (Li-Ion) batteries were recently introduced as an additional chemistry alternative. This article will help users make an informed decision when selecting among NiCd, NiMH, and Li- Ion (Lipo) batteries. All chemistries have advantages and disadvantages that must be weighed before choosing a battery pack chemistry.

Battery Characteristics

NiMH batteries provide the following advantages over NiCd:

• Higher capacity

• Limited memory effect

• Environmentally friendly

NiCd batteries provide the following advantages over NiMH:

• Longer cycle life

• Wider range of operating temperatures

• Lower price

Li-Ion batteries provide the following advantages over the Nickel chemistries:

• Light weight

• Environmentally friendly

• No memory effect

• Highest energy density of the three chemistries

Choosing a Battery Type

Table 1 shows key parameter comparisons of NiCd, NiMH, and Li-Ion batteries.Operating Parameters

1. Relative Capacity – Electrical capacity of the batteries when compared to a NiCd pack. M/A-COM determines the capacity of its battery packs by testing. Some third parties rate their packs by using individual cell specifications. Cell manufacturers rate cells based on a slow charge and discharge. In land mobile radio applications, batteries are charged and discharged much more aggressively and will not reach their rated capacity. Also, when cells are connected in series, as they are in all battery packs, it is impossible to extract the rated cell capacity from the pack.
2. Charge/Discharge Cycle Life – This represents the number of times a battery can be charged and discharged, which equates to the lifetime of the pack. Usage patterns can lengthen or shorten this number.
3. Memory Effect – The memory effect occurs when a battery pack is repeatedly recharged before it has been completely discharged. The result is that even after a full recharge, the battery will not allow its full capacity to be extracted. Memory can be minimized by conditioning. NiMH batteries are less susceptible to memory effect. Li-Ion is not susceptible to memory effect.
4. Conditioning – Conditioning entails fully discharging and then recharging a battery 3 or more times. This can be performed with a Cadex C7400 or iTech BC3506QP-5 battery conditioner available from M/A-COM. See the Cadex or iTech manuals for instructions on how to use the products.
5. Operating Temperature – This is the range of temperatures at which the battery can be reliably used due to characteristics of the chemical reactions involved. At lower temperatures, the battery is not able to convert its chemical energy into electrical energy. At higher temperatures, safety devices called positive temperature coefficient (PTC) resistors inside the battery prevent it from being used until the temperature falls. Batteries that are used in very cold or very hot conditions for extended periods of time can be permanently damaged.
6. Charging Temperature – This is the temperature range in which batteries can be charged due to limitations of the chemistry. All M/A-COM chargers limit charging outside of this range per cell manufacturer’s ratings. This often affects vehicular chargers because vehicle temperatures can vary to extremes.
7. Storage Temperature – If batteries are stored above or below their storage temperature range, permanent performance degradation can result. In short, batteries must not be stored in excessively hot or cold locations.
8. Storage Charge State and Duration – All cells degrade over time. Nickel packs should be stored in a fully discharged state. Li-Ion packs should be stored at 40% charge. Li-Ion packs should not be stored for extended periods of time (3 to 6 months from manufacture).
9. High-Temperature Susceptibility – Prolonged high-temperature discharge damages the organic materials for both NiCd and NiMH. High-temperature discharge can occur while a user is operating the radio in a high-temperature environment, or if the battery is stored in a high-temperature environment. Short exposure to high temperatures will not permanently damage the cells. Short-term performance will be degraded, but can be recovered through a couple of charge/discharge cycles at room temperature (typically 77°F or 25°C).
10. Self-Discharge – Self-discharge is the gradual loss of charge over time for an unused cell. It is directly proportional to ambient temperature. The higher the temperature, the faster the battery discharges. The lower the temperature, the slower the battery discharges.
11. Recycling – By U.S. law, NiCd batteries must be recycled. Currently, NiMH cells are recommended but are not required to be recycled. Li-Ion batteries are not required to be recycled.

Conclusion:

This article presents the advantages and disadvantages of NiCd, NiMH, and Li-Ion batteries for portable radios to help users make an informed choice when selecting batteries. NiCd batteries provide more recharging cycles, operate over a wider temperature range, and are lower priced than NiMH batteries. NiMH batteries have a higher relative capacity, limited induced memory effect, and are environmentally friendly. Li-Ion has a higher volumetric efficiency than the nickel-based batteries. Li-Ion batteries have no memory effect and are environmentally friendly. According to the lipo voltage, there are 3.7v lipo battery, 2s lipo battery, 3s lipo battery, ect.