The battery used to start the engine in a motorhome. It is usually only charged when the engine is running. It is separate and apart from the House batteries that are used to power various appliances in an RV. Only Motorhomes need a chassis battery.
The battery that is used to start the engine needs certain characteristics to give good service and long life. These batteries are noted for a high Cold Cranking Amp rating. This gives the battery the ability to turn a cold engine over and get it started. This is a measurement of how many amps a new, fully charged 12-volt battery can deliver at zero degrees Fahrenheit while maintaining a minimum of 7 volts.
Yes, that is a mouthful and what does it really mean? A battery with a high CCA rating is ideal for starting an engine. It provides the kick needed to give the engine the best chance of starting. To do this, it discharges fast. However, it also charges fast. These same characteristics make it a poor House battery. Yes, it can serve in that capacity for a short time in an emergency, but it is not intended for that use.
The Chassis battery is often used to power the RV Slides. It is charged by the alternator when the engine is running. On most RV’s, you cannot operate the slides while the engine is running. For this reason, it is sometimes beneficial to have a normal portable 12-volt battery charger to top the Chassis battery off after use when you are parked.