I bought one of those portable 12 volt electric coolers for my truck to keep cold sodas (Pop to you midwest boys and "cokes" for the Rebels) and was wondering if these cause a huge battery drain if left on for 5-6 hours while I'm at school?

Thanks Chet

 

In a word, YES. Depending on the size, these units will draw several amps (between 4 and 10). In a closed car that is in the sun, they will run practically continuously. A standard car battery has around 80-90 useful amp hours of capacity, so running a 5 amp load for 6 hours will take 30 amp hours (5 * 6 = 30), or a third of your battery capacity (and 5 amps is probably a small unit). With this much battery capacity drained away, starting the car could become a challange.

 

Could I wire in a 2nd 12 volt battery that was charged off the existing alternator and use this to power the cooler and if so, how would I do it? Will this 2nd battery over tax the alternator or provide double the volts (24) to my truck's electrical system?

Chet

 

Yes, a second battery could work. You would need to find a safe place to have it (a charging battery develops exposive hydrogen gas). A standard battery isolator will allow the second battery to be charged (your standard alternator charging circuit should be able to handle it), but not run down the main starting battery. Any boating or RV supply store (maybe even a Walmart) should have these devices. You want one rated for at least 10 amps. Should cost between $25 and $75. By now, you will be out over $100 for a battery and isolator. If this still makes economic sense, then by all means go for it.

 

mine draws 4.5 amps on cold and 4 amps on heat. i have run mine for 24 hours during the summer while camping with no ill effects. the battery was a little discharged but it worked fine.

 

Those coolers won't work very well in a hot enclosed cab; they can only produce a limited temperature differential of "up to 40 degrees F" (Koolatron's words). So if the cab hits 110 F in the sun, your "sodas" will be warm enough to swim in.
To get the most from this type of cooler, insulate the @#$% out of it to keep the cold in. Put a small fan inside to circulate air over the cooling fins and around your beverages. Arrange a duct so the thermoelectric unit gets cooler air from outside (underneath the bed?), and duct the waste hot air outside. Set up a thermostat to shut the power off if the incoming air gets too hot. I'm not sure if it smarter to use an absolute temperature or to work off the difference between inside the cooler and outside air. Maybe just get it as cold as possible in the early AM (or at night), then trust the insulation to maintain the cold the rest of the day.
Another potential problem: if you don't have a long enough drive to recharge the battery fully, you may have an unpleasant surprise after some days when you turn the key to start.
All things considered, blocks of ice from the freezer at home have a lot to recommend them.
Or buy an Engel cooler: they have a real refrigeration unit that is way more efficient and effective than the solid-state coolers. They also start at over $400 new.

 

390Gashog and angus are both correct, The unit does not completly kill my battery in the 5 hours I'm at school, however even on mild 70-80 degree days in the sun the beverages will not stay cool. May have to try and place the electric cooler in a styrofome cooler

Chet