Rechargeable batteries are those batteries that can be recharged again after discharge. You can find these batteries in your cordless tools, laptops, computers, cordless phones, and smartphones, etc. Rechargeable Batteries are also called as Secondary batteries.
Rechargeable batteries are of four basic types:
- Nickel-cadmium (Ni-Cd),
- Nickel metal hydride (Ni-MH)
- Lithium-ion (Li-Ion)
- Lithium polymer (Li-Po)
These batteries look similar from outside but there are significant differences between them. Let us have a look at different types of rechargeable batteries.
1. Ni-Cd Batteries or NiCad battery
Ni-Cd battery has nickel oxide hydroxide and metallic cadmium as electrodes. Ni-Cd cells have a nominal cell potential of 1.2 volts (V).
Ni-Cd Batteries have been around the longest of these three types. They have a good capacity and hold a very stable voltage between charges as they are being discharged.
The major Disadvantage of Ni-Cd batteries is the memory effect (The decreasing useful time between charges for a rechargeable battery is due to what is called the memory effect).
Also, Ni-Cd batteries can only undergo a limited number of discharge-recharge cycles before they need to be replaced. They often last only one to two years.
2. Ni-MH (Nickel-Metal Hydride) Batteries
Ni-MH (Nickel-metal hydride) Batteries are a more recent development in rechargeable batteries.
They have many of the same advantages that the Ni-Cd batteries have. However, they suffer much less from the memory effect than Ni-Cd batteries. There is some memory effect with Ni-MH batteries, but not nearly as much as with Ni-Cd.
Also, they can go through more discharge-recharge cycles than Ni-Cd batteries. Their typical useful life is more like 3 to 4 years. On the downside, Ni-MH batteries discharge more when not in use than Ni-Cds.
After about a week of not being used, a fully charged Ni-MH battery will have lost about 20% of its charge. Also, Ni-MH batteries cost more than Ni-Cd batteries, but their longer life tends to more than compensate for that.
3. Li-Ion (Lithium Ion) batteries
Li-ion (Lithium Ion) batteries are the next newest type rechargeable battery in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. Li-ion batteries are popular for portable electronics, with a high energy density, tiny memory effect, and low self-discharge.
Li-ion (Lithium Ion) batteries have the advantages over Ni-Cd and Ni-MH batteries and have a longer useful life. They do not suffer at all from the memory effect that is a problem for Ni-Cd and to a lesser extent for Ni-MH batteries.
The main disadvantage with Li-Ion batteries is that they lose about 10% of their useful capacity each year of use. This loss is due to the chemical breakdown of the cells and currently, there is no way to prevent or reverse this.
Li-Ion batteries typically last through about 300 to 500 discharge cycles or about four to five years.
4. Li-Po (Lithium Polymer) Batteries
Lithium Polymer Battery is a rechargeable battery of lithium-ion technology using a polymer electrolyte instead of a liquid one.
Lithium Polymer or LiPo batteries are a great new way of storing energy for portable devices from cell phones, home electronics to RC hobby battery packs used in cars, boats, and flight. These batteries provide a higher specific energy than other lithium-battery types.
The voltage of a LiPo cell depends on its chemistry and varies from about 2.7-3.0 V (discharged) to about 4.20 V (fully charged).
LiPo batteries are great because they can store 350% (approximately) more energy than a typical NiCd/NiMH battery pack and weigh 10% – 20% less. They can also discharge more current than a NiCd/NiMH battery and can be fully charged in about an hour.
Li-Po batteries have an advantage as they don’t develop memory or voltage depression characteristics like NiCd/NiMH batteries and do not need to be discharged before being charged.