Diesel VS Electric Auxiliary Power Units (APUs)

Adding an auxiliary power unit to your truck seems to be the only way to go nowadays. Constantly idling your truck to keep the air conditioning/heater going is not only bad for your engine but is also illegal in many states and cities. By installing an APU on you truck you are removing the need for idling during overnight stays or even during a long wait at a dock. With the APU you can shut that engine off and let the power unit take over while you can still enjoy that comfortable temperature and even watch a movie on your television.

There are quite a few choices when it comes to selecting an APU though. What brand or manufacturer do you go with? What type of brand do you go with? Do you get an Electric? Diesel? Hybrid? In this article we are going to take a look at the differences between these diesel and electric APUs and exactly what type you need based on your job conditions. Let’s dive in and take a look:


Even today the most common APU you are going to run into is diesel or combustion based. These include some of the big brand names in the APU market such as Thermo King, Carrier, Rigmaster, Cummins, Centramatic, and many others. A diesel APU comes with a specific set of advantages and disadvantages. The first big selling point is that a diesel engine can run indefinitely or until your fuel tank is empty. They can also typically power much more equipment then a standard electric APU.

The downside of diesel is that they can be loud. Now, not as loud as an idling truck engine, but still loud. In most cases though this isn’t a problem as a truck stop isn’t the quietest of places in the first place. The other downside of diesel is that it will require more maintenance then their electric counterparts. This is an engine that you are running and depending on the brand you will require maintenance between five-hundred to two-thousand hours of use. This can include changing the oil, belts, and other moving parts.

It is recommended that diesel APUs be used by long haul truck drivers. Say you have hit your hours for the day and need a place to stop for the night. Your diesel APU will be able to provide you power for the entire night without issue. In some cases if you have a twenty-four hour layover until your next pick-up/drop-off your diesel APU can come to rescue as well. Remember, that this APU uses only about twenty to twenty-five percent fuel then your standard truck engine does.


The concept of the APU is to give the truck driver an alternative means to power their vehicle other then idling their engine. Remember, that all of this was needed due to environmental concerns. The States saw their anti-idling laws as cleaning up the environment. Going with an electric APU is by far the most environmentally friendly of the APUs. There is no noise and no fuel consumed when using these battery powered APUs.

The big downside of these APUs though is that because they are battery powered they have a limited run time and can also only power so much before being maxed out. When you do run out of juice you have to wait hours before the system can be recharged again. The average electric APU can provide you with around ten to twelve hours of air conditioning time and a bit longer for heating (This excludes extreme conditions like Minnesota in January or Phoenix in August). You will also impact your run time if you decide to power other appliances such as a microwave, coffee maker, or even a television.

When the APU is drained and needs to be recharged it will typically take anywhere between six to twelve hours before the system is fully charged and ready to go again. If you couple this recharge time along with the limited run time and limited power supply it is recommended that electric APUs are used by small cab drivers on shorter trips. A long haul driver with a full sleeper would not have the best experience with an electric APU.

For an example scenario where this would be needed, say you are on site waiting to drop-off or pick-up but there is a one to two hour wait before you can even get tot he dock. This is a great opportunity to use the electric APU as you will only be using it for a few hours at a time. Then, when you start your truck back up the batteries will begin to recharge. Just remember that for a few hours these work great but if you plan on spending the night and running the APU for twelve hours then you are most likely going to need a diesel system. Also consider what climate you will be driving in mostly. If it is going to be an extreme climate like say Arizona or Maine then you should probably go with a diesel APU.


These systems did not get as popular as many folks would have hoped. The concept behind them is that they function as an electric APU until the batteries get too low on their charge and then the APUs diesel engine kicks on. The engine charges the batteries back to one-hundred percent and then the engine shuts off again. This process continues. The idea behind this is to not be running the diesel APU engine constantly and instead on an as needed basis.

This allows for fuel savings and a more environmentally friendly system. The downside here is that I could not find much literature or articles on the topic of hybrid APUs. The most recent article I found on this was back in 2006 and as you can imagine it was quite dated. If you know anymore about these types of models please reach out to me and I can update this article with more information.


As stated earlier, the diesel APU is king and will most likely will be for the foreseeable future. While the electric can you get you through those long waits at the dock or port they cannot provide you with the constant comfort for overnight stays. On the inverse though those diesel APUs will require maintenance down the road while the electrics have far less moving parts and require less maintenance. If it was up to me though folks I would choose the diesel every time. The diesel I know is going to get me through the night whereas the electric may run out of charge partway through the night.

I hope this article was helpful and thanks for reading,

Alec Johnson


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