E7440 battery question

I need a new battery so that the laptop can last a whole day. Currently my laptop has a 3-cell 34Wh 11.1V 2950mAh battery. Ive been told that a 6-cell and 4-cell would be compatible with my laptop. The 6-cell specs: 54Wh 7.4V.

My questions are: will the lower voltage affect my computer? Will it effect performance in anyway? Will the laptop heat up more or less? Basically, will it effect anything thats not battery life. 

Thanks