as represented in fig1 , the battery - operated auxiliary power unit (“ apu ”) 11 provides supplementary temperature control of a vehicle cabin using an additional independent air conditioning and heating system , the system is powered by an auxiliary battery pack ( abp 131 ) at night without placing a load on the regular truck batteries , but is sufficiently charged by an alternator while the operator is driving during a normal shift . the apu 11 comprises : batteries 103 configured in an auxiliary battery pack ( abp ) 131 and installed in battery box 135 , heating element assembly 109 , circulation pump 107 , temperature sending unit 111 , filler neck 113 , stock compressor 115 , drive motor 105 , optional electric compressor 117 , optional alternator 121 to charge the abp 131 , and optional mineral oil 140 as the heating fluid . the abp 131 is a battery pack that can be configured any number of ways , but as currently designed , the abp 131 comprises four deep - cycle batteries 103 connected in parallel to provide a 12v , 1000 a - hr , ten - hour power source . the abp 131 is installed in a frame - mounted battery box 135 , as shown in fig2 . the battery box 135 is mounted between the frame rails behind the sleeper cabin and in front of the fifth - wheel trailer hitch . all semi trucks have this space available with no other equipment mounted in this location . the current design places half the batteries on each side of the abp 13 , leaving the center section of the box open for installation of other equipment , such as a relocated a / c stock compressor 115 and drive motor 105 , or a completely new electric compressor 117 . as previously discussed , the truck &# 39 ; s stock four batteries will remain in use and are not part of the apu 11 . these truck batteries require a 130 - amp alternator to keep them property charged . federal law prohibits commercial operators from driving longer than eleven hours of a 14 - hour period , so with the four additional batteries comprising the abp 131 , the truck &# 39 ; s alternator must be able to fully charge all eight batteries while the truck is running down the road in an eleven - hour driving period , such that the abp 131 has sufficient power to supply the heating / ac system , and any other electronic devices during the off - period . in practice , the inventor has determined that the system will function well when the alternator 121 can provide 250 a of charging current to the two sets of battery packs . however , this replacement may not be necessary , depending upon the ambient temperature where the truck is operating and other conditions . this apu will not replace the truck &# 39 ; s front cabin heater . the front cabin heater will still provide front cabin heat and windshield defrosting functions . these two functions will only be required while the truck is driving down the road , so the apu 11 will not need to interfere with this bullet - proof system . the apu 11 includes heating element assembly 109 and the magnetic - driven impeller circulation pump 107 for sleeper cabin heating . the heating element assembly 109 , as currently designed , uses two 20 w heating elements , and is mounted inside the heating fluid reservoir which is plumbed directly into the heater core and in line with the circulation pump . this entire assembly is mounted in a housing with the attached blower fan , which is connected to the sleeper compartments ductwork . this assembly is typically located under the bed , inside the sleeper compartment and is not connected to the trucks drive motor cooling system . in operation , the heating element assembly 109 and magnetic - driven impeller circulation pump 107 are mounted in this housing to distribute heated mineral oil through the heater core . the stock blower fan is also mounted to the top of this housing , which circulates the hot air from inside the housing throughout the sleeper compartment via stock truck ductwork and this in turn heats the sleeper compartment . the new system continues to use the stock housing , heater core , ductwork and blower fan . the 12 v pump is rated continuous duty and uses magnetic power to turn the impeller . the impeller is not connected but floats freely in the pump casing . this means no leaking through a seal since there is no driveshaft connecting the pump motor and the impeller . as shown in fig3 , the heating element assembly is controlled as follows : a ) a user activates the heating operation through the use of the truck &# 39 ; s stock temperature controller , which energizes the heating element assembly 109 , consisting of two 20 w resistive heating elements ( both are energized to bring system to operating temperature and only one element is required to maintain operating temperature ), and the circulation pump 107 . the pump 107 continuously circulates the heating fluid while the heating system operates . b ) the temperature sending unit 111 provides a temperature reading for the truck &# 39 ; s stock temperature controller , which deactivates the second heating element through the use of a solenoid ( normally open switch ) when the mineral oil 140 ( or whatever heating fluid is employed in the system ) reaches a preset maximum setting . the solenoid changes state again ( closing the switch ) to reenergize the second heating element if the temperature of the oil 140 lowers to the preset minimum setting . c ) throughout the heating cycle , the circulation pump 107 circulates the heated oil through the stock heater core and the oil reservoir ( which houses the dual heating elements ). d ) the user ceases operation through the use of the truck &# 39 ; s built - in temperature controller , thus de - energizing the pump 107 and heating element assembly 109 . typical vehicle heating systems circulate water or an antifreeze through a heater core , but this invention optionally uses mineral oil 140 instead of antifreeze , because it has a higher boiling point than antifreeze or water and is noncorrosive . the mineral oil 140 circulates through the heater core with the use of the circulation pump 107 . the mineral oil 140 is added to the system through filler neck 113 , and circulated through the heater core and is heated with the heating element assembly 109 ( instead of the diesel engine ) and pumped through the heater core and copper piping which houses the heating element assembly 109 and circulation pump 107 . this entire heating system is mounted inside the truck &# 39 ; s standard housing ( typically mounted under the bed ) and is not connected in any way to the diesel engine &# 39 ; s cooling system . the air conditioning system is an optional element of the apu 11 . though the discussion assumes that the stock compressor 115 is moved from the engine compartment to the battery box 135 and powered by a drive motor 105 , the invention includes multiple configurations . the air conditioning function of the apu 11 can provide air conditioning for the front cabin and the sleeper compartment . the invention could be a retro - fit to a stock truck , or could be a manufacturer option . the invention can be installed and configured in at least two different ways , including : a ) two compressor option — two different a / c compressors , the engine - connected stock compressor 115 and a separate 12v electric motor driven compressor 117 installed in the battery box 135 driven by the abp 131 ; or b ) relocation option — the single stock a / c stock compressor 115 moved to the abp battery box 135 and driven by a drive motor 105 . the preferred approach is to relocate the stock compressor 115 from the diesel engine where it is typically belt - driven in the engine compartment under the hood of the truck , to the center section of the battery box 135 and driven by a 12v electric drive motor 105 . the same housing which holds the stock heater core and blower fan also hold the truck &# 39 ; s stock evaporator core for air conditioning the sleeper compartment . in operation , a user controls the a / c portion of the system ( through the use of the truck &# 39 ; s temperature controller unit ), which energizes the 12v electric drive motor 107 , which turns the a / c compressor 115 to increase the pressure of the refrigerant . the only unique part of this system is the use of the drive motor 107 to operate the compressor . as in most traditional a / c systems , when the refrigerant enters the evaporator the tubing size is increased which causes a rapid cooling of the refrigerant and the evaporator core as well . the sleeper compartment air is circulated through the housing ( via the use of the blower fan and ductwork ) where cold air is created and thus cools the sleeper compartment . while this invention has been described as it is currently built , the invention is not limited to the disclosed embodiments , but can be employed in various equivalent arrangements included within the spirit and scope of the claims .