I have been running lithium batteries for about 2-1/2 years. I built my own using CALB cells which are about half the price of battle born. They rate them for usable amp hours. (like battle born ) so yes a 100ah battery will give you a usable 100ah.
Here is a thread on my lithium battery build. I am in the process of relocating these cells into a new 5th wheel trailer. I am adding a BMS to the bank now as they are readily available and fairly inexpensive.
Drop-ins like battle born and Lion are a good way to go if you want the simplicity of a direct replacement. You will get better performance with lithium specific chargers but std chargers won't damage them as the BMS will protect the battery for over/under voltages and frozen cells.
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29476636.cfm
