The battery architecture for our project had to be carefully considered and chosen. Three types of rechargeable batteries were looked at: Nickel-Metal hydride (NiMH), Nickel Cadmium (NiCd) and Lithium-ion (Li-Ion). Each type of battery architecture has advantages and disadvantages which had to be weighed before choosing which type of battery would best suit our project. A comparison table of the three battery types can be seen below. Lead acid batteries were not considered for this project as they are relatively heavy and storage for our system may be a problem if lead acid batteries were used. Lead acid batteries also have the disadvantage of slow charging times up to 14 hours. Lead acid batteries are more appropriate for use projects with much bigger power applications. 
Nickel –Cadmium (NiCad) 
NiCad batteries have several benefits over the other battery architectures available today. NiCad batteries have the ability to be charged in a fast and simple manner even if they have been stored for long periods of time. They have a long shelf life no matter what the state of charge of the battery. If the batteries are badly treated they are quite forgiving. One big advantage of this type of battery is that it is the cheapest battery type in terms of the cost for every cycle. NiCad batteries cost approximately $0.04 per cycle. They are also quite efficient with efficiency ranging from 70 to 90%. However there are big drawbacks to this type of battery architecture. Firstly they have a large self-discharge rate of 20%/ month. NiCad has the lowest gravimetric energy density of all battery architectures at only 45-80Wh/kg. NiCad batteries can be prone to the memory effect. This occurs when the battery has been continually recharged before being fully discharged. This means that even when the battery has being fully recharged, the batteries will not allow the full capacity to be extracted. The overall result of this is a lower overall capacity for the battery. Conditioning must be done and the battery must be periodically exercised to prevent this memory effect.
Nickel-Metal Hydride (NiMH)
Nickel metal hydride batteries have a much higher gravimetric energy density than NiCad batteries operating in a...