An electric battery is a source of voltage or more formally source of electrical energy. Battery provides electrical energy by internal chemical reaction. Battery is a two terminal device. One is call positive terminal (+V) and another is negative terminal (-V) or ground. Generally batteries are two types.
Primary batteries are used once and discarded. Secondary batteries can be discharged and recharged multiple times. Batteries come in many shapes and sizes, from miniature cells used to power hearing aids and wristwatches to battery banks the size of rooms that provide standby power for telephone exchanges and computer data centers. According to battery chemistry battery can be many types. Several common types of battery used in robotics and tech project are discussed below.
1.5 V battery
Different size 1.5 V battery are available. Most common sizes are AA and AAA. Capacity range is 500 to 3000 mAh.
3 V Lithium coin cell
Coin-shaped cells are thin compared to their diameter.All these lithium cells are rated nominally 3 volts (on-load), with open circuit voltage about 3.6 volts. Capacity may very from 30 to 500 mAh. Extensively used in wearable device for their tiny size.
These batteries are not re-chargeable and could be used in small robots.
Nickel-Metal Hydride (NIMH)
These batteries, has a high energy density, and can be charged quickly. Another important feature is the price. NIMH batteries are cheap for their size and capacity. This type of battery is frequently used in robotic applications.
3.7 V Li-ion and Li-polymer
Lithium ion and lithium polymer batteries are rechargeable. They have high discharging capacity, high energy density, high capacity and small size. Li-polymer battery are used extensively in robotics and RC project. Specific energy of Li-poly battery is 100–265 W·h/kg.
9 V battery
Nine-volt battery in its most common form was introduced for the early transistor radios. It has a rectangular prism shape with rounded edges and a polarized snap connector at the top. They all have a rectangular shape; the dimensions are height 48.5 mm, length 26.5 mm, width 17.5 mm (or 1.9"x1.0"x0.68"). Both terminals are at one end and their centers are 1/2 inch (12.7 mm) apart. Capacity is around 600 mAh.
Lead Acid batteries are the workhorse batteries of industry. They are incredibly cheap, rechargeable, and easily available. Lead acid batteries are used in machinery, UPS's (uninterruptable power supply), robotics, and other systems where a lot of power is needed and weight is not as important. Lead acid batteries come in 2V cells, that means you can have a battery with an even number of volts. The most common voltages are 2V, 6V, 12V and 24V.
Series parallel connection of battery
Battery can be connected to series or parallel. When connected in series the voltage level increased and when connected on parallel the current capacity increased.
Two important things of battery:
Battery Capacity: Battery capacity is a measure (typically in Amp-hr) of the charge stored by the battery, and is determined by the mass of active material contained in the battery. The battery capacity represents the maximum amount of energy that can be extracted from the battery under certain specified conditions. However, the actual energy storage capabilities of the battery can vary significantly from the "nominal" rated capacity, as the battery capacity depends strongly on the age and past history of the battery, the charging or discharging regimes of the battery and the temperature.
Battery capacity is measured in either watt-hours (Wh), kilowatt-hours (kWh), ampere-hours (Ahr) or milliampere-hour (mAh). A Watt-hour is the voltage (V) that the battery provides multiplied by how much current (Amps) the battery can provide for some amount of time (generally in hours). Voltage * Amps * hours = Wh. Since voltage is pretty much fixed for a battery type due to its internal chemistry (alkaline, lithium, lead acid, etc), often only the Amps*hour measurement is printed on the side, expressed in Ah or mAh (1000mAh = 1Ah). To get Wh, multiply the Ah by the nominal voltage. For example, lets say we have a 3V nominal battery with 1Amp-hour capacity, therefore it has 3 Wh of capacity. The battery capacity will be better with lower drain currents. To determine the battery life, divide the capacity by the actual load current to get the hours of life. A circuit that draws 10 ma powered by a 9 volt rectangular battery will operate about 50 hours: 500 mAh /10 mA = 50 hours.
In many types of batteries, the full energy stored in the battery cannot be withdrawn (in other words, the battery cannot be fully discharged) without causing serious, and often irreparable damage to the battery. The Depth of Discharge (DOD) of a battery determines the fraction of power that can be withdrawn from the battery. For example, if the DOD of a battery is given by the manufacturer as 25%, then only 25% of the battery capacity can be used by the load.
The charging/discharging rates affect the rated battery capacity. If the battery is being discharged very quickly (i.e., the discharge current is high), then the amount of energy that can be extracted from the battery is reduced and the battery capacity is lower. Alternately, is the battery is discharged at a very slow rate using a low current, more energy can be extracted from the battery and the battery capacity is higher. For example, a coin cell that is rated for 1 Ah can't actually provide 1 Amp of current for an hour, in fact it cant even provide 0.1 Amp without overextending itself. Its like saying a human has the capability to travel up to 30 miles: of course running 30 miles is a lot different than walking! Likewise, a 1Ah coin cell has no problem providing a 1mA for 1000 hours but if you try to draw 100mA from it, it'll last a lot less than 10 hours.
The temperature of a battery will also affect the energy that can be extracted from it. At higher temperatures, the battery capacity is typically higher than at lower temperatures. However, intentionally elevating battery temperature is not an effective method to increase battery capacity as this also decreases battery lifetime.
C-rate: The charge and discharge current of a battery is measured in C-rate. Most portable batteries, with the exception of the lead acid, are rated at 1C. A discharge of 1C draws a current equal to the rated capacity. For example, a battery rated at 1000mAh provides 1000mA for one hour if discharged at 1C rate. The same battery discharged at 0.5C provides 500mA for two hours. At 2C, the same battery delivers 2000mA for 30 minutes. 1C is often referred to as a one-hour discharge; a 0.5C would be a two-hour, and a 0.1C a 10 hour discharge.
The capacity of a battery is commonly measured with a battery analyzer. If the analyzer’s capacity readout is displayed in percentage of the nominal rating, 100 percent is shown if 1000mA can be drawn for one hour from a battery that is rated at 1000mAh. If the battery only lasts for 30 minutes before cut-off, 50 percent is indicated. A new battery sometimes provides more than 100 percent capacity. In such a case, the battery is conservatively rated and can endure a longer discharge time than specified by the manufacturer.
Charge rate is often denoted as C or C-rate and signifies a charge or discharge rate equal to the capacity of a battery in one hour.
A battery charger may be specified in terms of the battery capacity or C rate; a charger rated C/10 would return the battery capacity in 10 hours, a charger rated at 4C would charge the battery in 15 minutes. Very rapid charging rates, 1 hour or less, generally require the charger to carefully monitor battery parameters such as terminal voltage and temperature to prevent overcharging and damage to the cells.
How Batteries Are Measured
This is pretty straight forward, how big are the batteries? Lead acid batteries don't get much smaller than C-cell batteries. Coin cells don't get much larger than a quarter. There are also standard sizes, such as AA and 9V which may be desirable.
Weight and power density
This is a performance issue: higher quality (and more expensive) batteries will have a higher power density. If weight is an important part of your project, you will want to go with a lighter, high-density battery. Often this is expressed in Watts-hours per Kilogram.
Price is pretty much proportional to power-density (you pay more for higher density) and proportional to power capacity (you pay more for more capacity). The more power you want in a smaller, lighter package the more you will have to pay.
The voltage of a battery cell is determined by the chemistry used inside. For example, all Alkaline cells are 1.5V, all lead-acid's are 2V, and lithiums are 3V. Batteries can be made of multiple cells, so for example, you'll rarely see a 2V lead-acid battery. Usually they are connected together inside to make a 6V, 12V or 24V battery. Likewise, most electronics use multiple alkalines to generate the voltage they need to run. Don't forget that voltage is a 'nominal' measurement, a "1.5V" AA battery actually starts out at 1.6V and then quickly drops down to 1.5 and then slowly drifts down to 1.0V at which point the battery is considered 'dead'.
Some batteries are rechargable, usually they can be recharged 100's of times.
Which battery is perfect for your project?
You see there are many types of battery and many types of battery chemistries, so it's not easy to decide on which solution is best for your project. If your project is very power-hungry such as large sound systems, and motorized projects you can select lead acid battery. If you want to build wearable project and required small power you can select lithium coin cell. For any portable light weight project which need moderate power you can select lithium-ion battery. You can also choose cheaper Nickel-Metal Hydride (NIMH), a little heavier in weight compare to li-ion. If you like to make power-hungry RC quad-copter or like that probably Lithium Ion Polymer(LiPo) would the best option for you because these batteries have small dimensions, are lightweight compared with other types of batteries, can be recharged very quickly, and has a high current output.
If your battery need to be user replaceable then you should select universal AA, AAA or 9V battery. If you require 5V battery then you can use 3 AAA or AA alkaline cells (4.5V) or 4 NiMH cells (4.8V). Be sure your device will run at these slightly lower voltages (most probably it does).
Want your rechargable batteries to last a long time?
Use a high-quality charger that has sensors to maintain proper charging and trickle charging. A cheap charger will kill off your cells.
If you need battery holders or battery clips, you can have a look at these products: