Battery and Charging Technologies

Battery Technologies

Alessandro Volta pioneered the primary electric cell at the turn of the 19th Century. It wasn't until 1859 that the first rechargeable battery was created. It's inventor, Gaston Plante, employed a Lead Acid chemistry. It would take another 40 years before the advent of the nickel-cadmium battery. This was an open design and wasn't economically viable due to high material costs. The Ni-Cd battery was successfully sealed in 1947 and has been used in a variety of applications ever since. The nickel-metal hydride battery became commercially available in the late 1980's. The early 1990's saw the release of the rechargeable lithium based cells. The unstable nature of lithium led to the development of the safer non-metallic lithium ion chemistry.

Each battery chemistry has its own strengths and weaknesses. The following section provides a brief overview of the different chemistries available for the portable radio users.

Ni-CD Battery

Nickel-cadmium batteries have been the workhorses of the professional mobile radio industry since its inception.

The mature battery chemistry is the most robust of all and has the widest operating temperature range. Ni-Cd batteries can accept the fastest recharge rate and is the best value in terms of initial cost and the total number of charge/discharge cycles. The main limitation associated with Ni-Cd batteries is its susceptibility to the 'memory' effect. This results in low capacities and unreliable performance. The chemical processes that contribute to 'memory' are caused by outdated charging methods and compunded by poor user discipline.

Ni-MH Battery

Nickel-metal hydride batteries became popular in the late 1980's.

They were sold at the time as the solution to the traditional shortcomings of the Ni-Cd chemistry. Time has shown that Ni-MH does indeed provide a few marginal improvements over Ni-Cd. However it could be argued that the additional drawbacks of the Ni-MH negate these benefits.

Ni-MH batteries are still prone to memory though generally not to the same extent as Ni-Cd. The Ni-MH chemistry allows for a higher energy capacity than Ni-Cd but provides fewer charge/discharge cycles. The performance of the Ni-MH batteries can drop dramatically after a few hundred cycles especially when high load currents are used. This phenomenon is caused by an increase in the battery's internal resistance. Ni-MH batteries have a higher self-discharge rate and take longer to charge than the Ni-Cd alternative.

Li-Ion Battery

The Lithium-Ion chemistry and its variants offer the highest energy densities currently available.

This capability has allowed the size of handsets to be drastically reduced. Most modern mobile phones operate from just a single cell. Replacement Li-Ion batteries are now offered for many handheld radio handsets and are provided as standard for the latest digital handsets.

While this chemistry has the lowest self discharge rate the actual cells tend to deteriorate relatively quickly over time. Battery capacity can worsen to such an extent that failure is not uncommon within 1-2 years. To combat the aging process, manufacturers recommend that Li-Ion batteries be partially charged and stored at 15C. The major drawback with Lithium based chemistries is the inherent fragility of the materials used. For safe operation, Li-Ion batteries are built with a protection circuit. This monitors the cell's temperature and limits the input and output voltage and current. Li-Ion's recent introduction into handheld radio usage coupled with the requirement for a protection circuit means that it is currently the highest cost chemistry for portable mobile radio.

Summary

Battery Charging Technology

Historically portable radio users have had little choice when their batteries need to be recharged.

Some methods still used today can be traced back to the invention of the rechargeable battery. While conventional charging techniques successfully put energy back into batteries they do not take into account the individual chemical state of each battery. In other words, traditional chargers simply push energy into the battery without regard to what the battery really requires.

The main problem with traditional battery charging is that the discipline of the operator must be relied upon to ensure the procedure is carried out to the best effect without degrading the battery. OEM chargers detail a variety of rules that need to be followed. Few users have the time or the patience to stick to the complicated regime recommended by manufacturers. As a result, many organisations invest significant resources on battery management to combat the problems caused by antiquated charging methods.

The following section gives a brief overview of the different battery charging methods available.

Trickle Charger

The trickle or slow charger is the standard unit provided by most handset manufacturers.

The unit works by pushing a steady current into the battery at a rate which is normally 10% of the battery's capacity. So, for example, a 1700 mAh battery will be charged at 170 mAh. Typical charge times range from 8 to 12 hours.

It is left to the user to terminate the charge at the correct time. Failure to remove the battery from the charger means that more energy enters the battery than it can absorb. It causes a host of degenerative chemical processes within the battery that lead to reduced capacities and premature failure. In the worst cases the temperature inside the cells will become so high that the battery vents off the gas build up.

Fast or Rapid Charger

As the name suggest, this type of charger is quicker than the standard trickle charger.

Rapid chargers work by providing a high rate of constant energy into the battery until a reference voltage is reached. Although the green ready LED illuminates the battery is usually only charged to 80% of its capacity. The charge is then dropped to a trickle rate that is approximately one tenth of the battery capacity. It is then up to the user to guess when the battery is charged to full capacity.

Many manufacturers stipulate that the battery should be left on the charger for between 1 and 2 hours after the green light comes on. With no termination the rapid charger has a tendency to quickly overcharge and damage batteries.

Pulse Charger

Pulse charging techniques were pioneered at the turn of the 20th Century with the last significant patent issued in 1967.

The patent has now expired and a variety of pulse chargers are available from a number of manufacturers. The pulse charger works by subjecting the battery to a sequence of pre-programmed current pulses. The advantage of the pulse charger is that it provides for rest periods during charge.

This type of charger can also help to break down dendrite growth, a contributor to the memory effect. However, pulse chargers do not take into account the internal state of the battery. They merely subject the battery to a series of repetitive pulses. Some units even revert to a potentially damaging trickle charge once the battery approaches full capacity.

ACT Intelligent Charging

Advanced Charger Technology has invested over $40 million to solve the battery problems experienced by professional mobile radio users.

The result is a unique, fully patented technology that actually responds to the chemical state of each battery. A charging and conditioning waveform is simultaneously applied to the battery ensuring the longest and most reliable performance possible. Another benefit of ACT's truly intelligent system is its charging and conditioning process is completely automatic and requires no intervention on the part of the user. There's no charging rules with ACT, simpy put the battery on and remove it at any time.