Lead Acid battery is a well-known energy source but cannot supply large amount of power in short time. Deep discharge at the time of cranking reduces the life of the battery drastically as compared to normal use. Extra factor of safety is provided for cold weather cranking performance, poor maintenance and end of life performance in view of deep discharge. Hence it is heavy and bulky. On the other hand, Ultracapacitors can supply large burst of power for short time but cannot store much energy. It is seen that in Hybrid Power pack (Ultracapacitor + down sized Battery) the major power requirement at the time of cranking is taken by Ultracapacitor resulting in reduced load on the battery thereby making it possible to be downsized.