The two gens are very similar.� The main differences are battery charging and warranty. 12HDKCD-2209 is a 12000 watt Commercial Mobile generator with battery charging. 12.5HDKCB-11506 is a 12500 watt RV generator with no battery charging. The RV generator is recommended for use in applications that have living area, sleeping quarters, and restroom and is not being used for business. Standard warranty for CM gen is 2 year/2000 hr. Standard warranty for RV gen is 2 years + 3rd year parts/labor on major power train and gen parts, however, if an RV gen is used in a CM application, it will not receive the full warranty.