Most "walmart style" battery chargers are a "one size fits all batteries" type of device. Most are "small chargers" so the novice user won't forget to monitor charging and either overcharge, boil off or burn up a small battery. Most converter/chargers in modern RV's are designed specifically for larger sized, deep cycle, low (or no) maintenance batteries. As such, they charge at appropriate rates to "clean the plates" as well as protect the batteries from damage from "slow charging" while effectively maintaining the battery bank in the RV.
Most WFCO converter/chargers installed in Keystone products are at least 55 amp systems. Usually 30 amps of that is dedicated to battery charging at 3 levels of charge. If the demand for the the converter output (the other 25 amps) is consumed by the "house 12 volt circuits" then the charge power is shunted from battery charging to house power.
Usually, except in very rare situations, plugging the trailer into a generator or into shore power will be the fastest, most economical and safest way to charge your batteries when dry camping. Your WFCO converter/charger will safely and efficiently charge your battery bank, usually faster than an "outboard system" and most definitely faster than a $39 WalMart automotive charger.
A 10 amp WalMart charger just can't compare with the "state of the art" converter charger installed in all Keystone RV's.
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS