TECHNICAL ASSISTANCE: BATTERIES
Here you will find some useful advice concerning the different battery types available from Twowayaccessories.com. If you have a specific question which is not answered here please e-mail us at techhelp@twowayaccessories.com or call us on 01332 513065
Battery Capacity
This is stated as the size of current (amps) that the battery will produce over a rated time (hours). Measured in mAh, (milliamps x hours) or, 1000 times bigger Ah, (Amp x hours).
This rating is usually lower if a battery is designed to produce a large current (i.e. if the battery has to work fast it will usually produce a little less useable energy). Note that 10 Ah at 12 volts is twice the energy of 10 Ah at 6 volts. The measure of energy stored by a battery is volts x amps x hours or watt hours
Battery Charging
Batteries are charged with a DC current, positive terminal to positive terminal. The voltage must be greater than the battery or battery pack voltage. The current must be limited and the current should cut off when the battery is fully charged.
Full charge is sensed either by a rise in voltage, a rise in resistance or a rise in temperature.
Battery chargers are designed to supply a suitable current for the batteries with which they were designed to work.
Unless chargers are labelled otherwise you should remove the battery after 16 hours. More sophisticated chargers will switch to a trickle when they sense the battery is fully charged. Nickel Cadmium [NiCad] and Nickel Metal Hydride [NiMh] batteries should not be left on trickle charge for more than a few days.
The charging current is approximately one eighth of the Ah (in amps) or mAh (milliamps) rating of the battery. A full charge takes about 1.4 times the label capacity.
E.g. NiMh Battery 1800mAh capacity
Charging current 1800 divided by 8 = 225 mA
Charging time 1800 divided by 225 x 1.4 = 11.2 hours
At no time should the temperature rise much beyond blood heat
Battery Disposal
Never burn any battery. It may explode, it will release caustic electrolyte, and it may distribute harmful metal oxide particles.
Batteries containing the following materials must be disposed of carefully:
- Lead
- Silver
- Cadmium
- Mercury
In the UK, the local authority usually has a facility where they accept domestic waste and will receive batteries handed in separately.
Lithium batteries containing more than 0.5gram of Lithium metal present a special hazard. Seek special advice. Contact techhelp@twowayaccessories.com.
Alkaline, NiMh, zinc-air, small Li-ion and Lithium coin cells can be disposed of in domestic waste
Battery Types
Lithium Ion Batteries [Li-Ion]
These are rechargeable batteries which are becoming more popular in two way radios. They are lightweight, high capacity and do not suffer from memory effect unlike NiCad batteries.
Li-Ion batteries are generally more expensive than NiCad or NiMh batteries and whilst there is not that much difference in capacity for the same volume as a NiMh battery, they are significantly lighter.
Li-Ion batteries can be 'top up' charged/recharged at any convenient time, without waiting for the battery to be completely discharged first.
For storage- store them as they are and allow them to self discharge slowly. Recharge them fully again when you want to use them.
Nickel-Cadmium Batteries [NiCad]
Nickel-Cadmium batteries are rechargeable. The most common battery pack used by two way radios. Due to their Cadmium content NiCad batteries must be disposed of safely. See Battery Disposal.
NiCad batteries can suffer from what is known as 'Memory Effect' which can reduce their voltage with age. The best practise is to charge the battery pack when a drop in power is noticed. If a battery pack is overcharged a risk of voltage reversal of the weakest cell can occur.
NiCad batteries should be stored as they are, and recharged before use. NiCad batteries self-discharge and can lose about 40% of their charge in 4 weeks.
Although this type of battery has a low internal resistance they can deliver a high current, they don't overheat easily in use and they can be charged quickly. Used sensibly they have a life span twice that of NiMh or Li-Ion batteries.
Nickel Metal Hydride Batteries [NiMh]
Nickel Metal Hydride. Batteries have complemented NiCad batteries and are generally about the same price. They have the advantage that no special disposal method is necessary and have increased capacity with less 'memory effect'
Sometimes slower charging than NiCad they should not be recharged until power begins to drop and they should be stored discharged.
Memory Effect
Some rechargeable batteries are said to have a memory. If they are part-used and recharged before the whole charge is used up, they 'remember' this and next time will only use that part of their capacity. Therefore part of their capacity is lost.
NiCad and NiMh batteries are said to suffer from memory effect.
NiCad and NiMh batteries prefer complete cycles; fully charge then use
until empty, do not recharge before storage - allow them to self-discharge
during storage.
In the real world, either of these batteries will accept less than the
ideal and provided that they are recycled completely, full to empty, reasonably
often they will put up with what comes in between.
NiMh batteries have less memory effect than NiCad batteries and in general
will out-last NiMh batteries. This is because NiCad batteries, under reasonable
conditions, will take more charge/discharge cycles.
Discharge
Batteries, stored unused, lose their charge (age), slowly with time.
The rate of self-discharge depends on the type of battery. Alkaline batteries
and most primary batteries have a good shelf life - they self-discharge
very slowly.
The rate of self-discharge rises rapidly with temperature, the ideal storage temperature is between 4 and 15 Deg. centigrade.
These are guide figures, for the loss of charge in 1 month at 20 Deg. C.
| Alkaline | Primary | >1% |
| Sealed Lead-Acid wet cell | Secondary | 11% |
| Sealed Lead Acid dry cell | Secondary | 9% |
| Li-ion | Secondary | 35% |
| Lithium Manganese Dioxide | Primary | 0.1% |
| Magnesium-Sea Water | Primary | >0.5% |
| NiCad | Secondary | 40% |
| NiMh | Secondary | 50% |
| Silver-Oxide | Primary | 0.5% |
| Zinc-Air | Primary | >1% |
| Zinc-Air, tab removed | Primary | 35% |
Temperature
Common batteries like the same temperature as humans. They won't work well in low temperatures and high temperatures shorten their life. This factor needs careful consideration if batteries are going to be relied upon in an emergency.
Store at a maximum temperature of 25C, preferably less. Special batteries are made for other temperature ranges and Li-Ion batteries perform the best of the common batteries.
As battery temperature rises so battery performance reduces. Working at high temperatures is bad for the battery. The cells are packed close together with no room for the heat to escape. NiMh cells with their higher internal resistance are more at risk than NiCad cells.
Voltage
The voltage of batteries is quoted as 'nominal' because it varies during the life of the battery and the amount of current being taken from the battery. If the voltage of a new battery is measured (across a large resistance) it may be a little higher. This will soon drop to the nominal voltage and later in life the voltage will drop further - the torch becomes less bright as the battery gets used up.
The voltage of alkaline batteries drops in a curve during its life.
Lead-Acid, Zinc-Air, Silver-Oxide and NiCad batteries have a much more constant voltage - a 'flat' discharge/time curve.