• Proper charging – Make sure you charge your battery properly using a quality battery charger.  For safety, make sure you put your batteries in a lipo bag while charging.   you can insure that if something goes wrong at least it will be contained.
• Don’t over-discharge – Make sure you stop using your battery before the voltage gets to the minimum cut-off voltage.
• Heat kills batteries – Don’t use batteries or charge batteries when they are warm. After you’re done using them, give them a little time to cool off before you charge them. And after you are done charging them, give them a little time before you use them.
• Proper storage – Do not store your batteries in a hot location.  Store lipo’s at the proper storage voltage. Swelling increased significantly after only 4 hours of storage when batteries were at a state of charge above 80%.

Here is some sound advice that is current. As with most internet information there is alot of OLD posts that relates to old battery technology

The decision appears to become less important as the technology advances. The best advice is to take care of the battery setup you have.

Short lifespan problems are caused mostly by the pilots careless and ignorant management this because most pilots have no idea about how to protect and extend the batteries lifespan

Never overcharge your battery

Charge your battery in time

Choose a larger capacity battery

This is the basics if you still want to consider adding an additional Battery

Make sure you Install a second battery of the same model/type/capacity :  Weight and Balance is critical to getting the drone tuned and flight performance maximized

Install a circuit board that converts/transfers the output for the desired affect   :  Use an adapter equipped with high quality electronics, designed for your desired performance goals.

Voltage = Flight time 
Amperage = Travel distance 

If you want more voltage (flight time), you need to wire 2 batteries in series,

If you want more distance  Then amperage is the way.  Wire the  2 batteries in parallel.  The configuration adds more charging time (50%) compared to series connection

Use only quality batteries of the same type and age   

If the battery has twice the capacity, but the drone has twice the weight, you won't be better off.

Reduce the whole drone’s weight

You can install the camera to the drone when it is needed. If you are just flying your drone to enjoy it and not trying to capture any video then leave the camera off. The camera will not only add more weight but it also drains the battery due to it needing to be powered to run. And the reducing weight will reduce the harm to the unit if it fails.

Buy a good quality brand like Tattu, Bonka or Turnigy
This is very important to have a longer lifespan of the battery. 

The decision appears to become less important as the technology advances. The best advice is to take care of the battery.

Short lifespan problems are caused mostly by the pilots careless and ignorant management  because most pilots have no idea about how to protect and extend the batteries lifespan

Never overcharge your battery

Charge your battery in time

Choose a larger capacity battery

Battery Technology is moving pretty fast for the drone community. We try to get into the dirt with battery tech in the forumla website but here we want to do this as it relates out the build.

This is the battery pack setup I chose. My intent was to connect to 6s together for some big voltage but Theory will apply in the decision so lets see