As smartphones and other network handheld devices become extremely important to our personal and professional lives, it becomes essential to squeeze out every last bit of battery life to remain connected. When using a tablet or smartphone to access the internet, you often have a choice between using 3G or WiFi to connect. In general, networking using 3G drains your device’s battery much faster than connecting with WiFi.
Signal Strength plays a key role in determining the battery life. If a connection is being tried to be established on either WiFi or 3G and if the signal strength is low, the transmitter of the smartphone will have to amplify the signal to high levels which increases battery usage. Similarly if the signal keeps dropping and the smartphone will have to scan regularly for either of the signals, the battery power would be used up significantly.
WiFi antenna in your smartphone has a typical range of few meters. It is designed to find the WiFi router withing that range only. So the signal power it takes should be enough to survive for few meter only.
On the other hand, for 3G data transfer, you need to send the signals to the receiving antenna which could be a upto a few kilometers from where you are. So the signal should be strong enough to survive few kilometers.
To give an idea, lets assume :
Your WiFi router is at a distance of: 3 meters,
and the 3G receiver antenna of service provider is at a distance of: 1 Km or 1000 meters
Now, in order to have the same signal strength at the receiver’s antenna of WiFi and 3G, the transmitted signal should be of ratio: (1000/3)^2 = 111000
Means, the 3G signal should be 111000 times stronger than WiFi signal, thus proving 3G data transfer consumes extra power.
The logic generally used by people is that WiFi has an additional radio chip and it uses more power, but that may not always be true. When WiFi is being used, the mobile data part is switched off automatically which in turns facilitate for a longer battery life.
So whenever possible use WiFi as it always helps.