How Much Current Is available in Series-Connected Batteries?
Connecting batteries in series will increase the voltage and keep current capacity constant. When you connect batteries in series :


Vtotal = V1+V2+...+Vn (e.g. 1.5+1.5+1.5=4.5V)
Current capacity = lowest current capacity between batteries (e.g. 2A)


Connecting batteries in parallel will increase the current and keep voltage constant.


Vtotal = single battery voltage (e.g. 1.5V)
Itotal capacity = Summation of all batteries current capacity (e.g. 2+2+2=6A)


You can use combination of connecting batteries in series or parallel to achieve your desired current capacity and voltage margin. This link will help you http://batteryuniversity.com/learn/article/serial_and_parallel_battery_configurations