Same guy as before.
You'll need to put your new lifepo4 battery into something protective to carry it. My prefered method is to construct a tight fitting protective box around the soft pouch cells. This protects the shrink wrapped soft cells from chafing or moderate impacts. Many materials can be used. My first pingbattery box was a cut and folded aluminum cookie sheet. Now I tend to use coroplast sheets. Coroplast is the plastic cardboard commonly used for political and real estate roadside signs.
Once you have it boxed up, I carry the battery a variety of ways. Metal toolboxes, panniers, or rack bags. Foam sheeting is used to shim the battery into the container to keep it snugly carried without flopping around.
The advantage of pouch type cell lifepo4 vs similarly priced or cheaper round cell lifepo4 packs is the reliablility of the contacts between cells. The soldered tabs of the pouch type take a bump much better than the cheaply tab welded round cells.
Quality constructed more expensive round cells are ok, such as A123's. It's not tab spot welding that is the problem, it's that the cheap cells are poorly tabbed.
In general, the round cells of any type will take up more space per AH, because of inevitable air space between stacks of round cells.
Whatever new battery you choose, you will need to attach a plug to it that matches your old battery. It may be easiest to change the plug on the controller itself as well. Rather than match the controller, change to a type of plug that you can put on both controller and the new battery.
4mm gold bullets are popular, as are anderson powerpoles.
THE LIPO RULES. NEVER ABOVE 4.3V NEVER BELOW 2.7V DON'T PUNCTURE
Ideal charging /discharging range for Lipo, 3.65v minimum 4.1v maximum
See battery technology section, FAQ thread at the top of the page for lipo noob info.