Fire and Ice
APU vs. battery power
Finding the right key-off system for your operation

By Jeff Barker, Land Line contributor

As idling regs spread like a red-hot wildfire across the country, the first alternative most operations grabbed for were auxiliary power units.

Unfortunately, in the early days some brands posed reliability issues. Coupled with the fact that some drivers got static for noise ordinances and California is now even regulating APU emissions, the industry started looking for another way to provide key-off livability in the trucks.

Today, there are more reliable engine-based APUs out there than there was. And there’s a growing trend toward battery-based auxiliary HVAC (heating, ventilation, air conditioning) systems.

All truck manufacturers now offer factory-installed battery-based systems.

There are pros and cons to using either type of system. Truck owners need to take their time to do thorough research on the types of auxiliary climate control systems available, and manufacturer specifications, to make an informed decision.

Over the years I have personally used both engine-based and battery-based systems in an over-the-road environment and have encountered various situations where I’ve found their limitations.

In fact, the 2010 International ProStar Eagle I’ve been driving this past year has what was originally known as the MaxxCool battery-based HVAC system. The more updated MaxxPower system was introduced in 2011 and boasts a built-in power inverter with two 120-volt outlets in the sleeper.




  • Reduced maintenance expense. There’s not an additional engine on a battery-based HVAC system that requires upkeep.
  • Quieter operation.
  • Can be set up to operate on shore power.
  • Less likely to be affected by any APU emissions regulations since they don’t utilize an engine.
  • If your truck is used in situations where it is rarely parked for more than 10 hours of bunk time and you don’t have many devices that generate hotel loads, then a battery-based HVAC system may work for you.


  • Lower Btu output, especially on air conditioning. If you’re parked in the sun on a hot summer day, particularly if your cab and sleeper is poorly insulated, then a battery-based HVAC system may not be able to maintain a comfortable temperature. I’ve found myself having to idle my truck engine to use the main air conditioning system when I was parked in extreme heat.
  • More weight: Most battery-based systems on average weigh more than an engine-based APU system. The system on my truck has a certified weight of 525 pounds as opposed to an average weight of 350 pounds for many engine-based APUs.
  • No way to maintain a charge on the truck’s starting batteries. No engine also means no means to spin an alternator shaft. There’s no way for these systems to provide more than a few hundred watts of 120-volt current, which would require the driver to run the engine and use a larger power inverter.
  • Battery-based systems can only run for so long until the batteries are discharged and the low-voltage cut-off shuts down the system. I usually get 8-10 hours of air conditioning and 12 hours of heating before the low voltage alarm goes off.
  • Battery-based HVAC systems utilize a bank of four auxiliary batteries that will eventually need to be replaced after many charge and discharge cycles have taken place.



  • Generally have a higher Btu output on the A/C side and with good air flow usually capable of cooling down a sleeper.
  • Can maintain the charge on the truck’s starting batteries and facilitate the use of a power inverter for the 120-volt current needed to run most appliances. Also, some units have a generator for that purpose and can even power an engine block heater if needed.
  • Most APUs are installed with their engine cooling circuit tied in with the truck engine’s cooling system and can keep the main engine warm without the use of a block heater. Some units can be set up to run with a stand-alone cooling system if you prefer to keep things separated.
  • Can operate indefinitely on the fuel available from the tanks.
  • If long layovers and 34-hour restarts are the norm, then you will be better off with an engine-based APU.


  • Some states are imposing restrictions on APUs. In fact, California requires a diesel particulate filter on any 2007 or newer APU that’s on a 2007 or newer truck.
  • Noise, more maintenance, and the engine will eventually wear out after so many hours of use. Reliability of some units with known design flaws is still a legitimate concern.
  • Cannot be set up to run on shore power (unless it uses an all-electric HVAC system like what is found on a Carrier ComfortPro APU).

The performance of most any APU or battery-powered HVAC system will depend on the sleeper size and on how well it’s insulated, not to mention how well the installation is done. If you have a large custom sleeper, you will need to look into a system with a higher Btu rating. Many of them need a roof-mount A/C unit with a rating of at least 15,000 Btus to work effectively. LL