The batteries are available in various shapes and sizes and generally the following are main parameters which need to be considered while selecting batteries:
1. Energy content or capacity: This is express in Ah (mAh).This is important characteristic that indicates how long the battery can last before it discharges and become useless. For a given battery type, the capacity also indicate the battery size. A battery with larger Ah rating will necessarily be bigger in volume than a similar Ah rating.
2. Voltage: This parameter is the voltage provided by battery.
3. Storage: This indicates how the battery needs to be stored, when not being used.
4. Self life: This parameter is a measure of how much time would a battery last before it discharges on its own. There is no point in buy a stock of batteries for next 10 years if self life of battery is, say only one year.
5. Operating temperature: Batteries have notoriously poor temperature characteristic. This is because working of the battery depends upon chemical reactions which are temperature dependent. Batteries perform rather poorly at low temperatures.
6. Duty cycle: The duty cycle of the battery indicates if the battery can be used continuously or not, without loss of performance.
There are two types of batteries:
- Primary batteries (non rechargeable)
- Secondary batteries (these can be recharged).
Primary batteries are those that can not recharge. Once they lose energy, they have to be replaced. Primary batteries are of different types. Most common are zinc chloride with carbon electrodes dry cells. The cell voltage is 1.5V. These are cheapest of all primary batteries. Increasingly, alkaline cell also of 1.5v are become popular. They have higher capacity compared to the zinc chloride with carbon electrode dry cells. The cell voltage is 1.5v are become popular. They have higher capacity compared to zinc chloride cells. Alkaline cell also have higher self life then the zinc chloride cells. Another type of primary battery is a lithium battery with cell voltage of 3.0v. These batteries are expansive compared to zinc chloride and alkaline batteries but have much higher energy density and self life of upto 10 years.
The secondary batteries have the advantage that they can be recharge after being discharge. Most popular of these batteries is the NiCD(nickel cadmium) and the lead acid batteries. The NiCD batteries have a cell voltage of 1.2V, the so- called 9V box type NiCD batteries are actually about 8.2v. the lead acid batteries have a cell voltage of 2V. Lead acid batteries of the so-called sealed variety are safe for use in portable instruments. Contrary to the lead acid batteries used in car, these do not pose any danger of leaking.
Lead acid batteries have higher energy density then NiCD. The lead acid batteries also have a relatively larger retention compared to the NiCD batteries.
Secondary batteries perform well if they are recharged regularly. If these batteries are discharged more then a certain minimum there operational life reduces drastically.
Batteries are charged at a fraction of there Ah rating. Typically lead acid batteries are charged at a 10th of the Ah rating of the battery. NiCD batteries, on the other hand are quite quirky. NiCD batteries are recommended to be initially charged at a 10th of Ah rating and then switched over to trickle charging at fraction (1/50) of the Ah rating.