Deep Cell Battery Charge

The coolers I'm familiar with use a small heat pump. (and aren't supposed to have any ice in them). I have an old one that either cools or heats and draws about 2 amps at 12v. That Coleman is rated for 4 amps. There are a number of systems used for RVs that will tie an extra battery in parallel to your main battery, but disconnect it when the car is off. Otherwise you're draining both batteries. The bigger question is where to put it, since having a battery in the passenger compartment is a no-no.. The Prius battery has positive pressure ventilation plus is vented to the outside.

 

Location of the battery is not a problem, if you buy the right "type" of battery, like an Optima AGM Blue-Top. We carry ours inside our Prius when we go camping - it's approved for use inside of occupied enclosures, aircraft, etc. since it has none of the safety issues of an old lead-acid battery - no venting needed, no battery box needed, no holes in your pants, etc. That said, due to electrical draw from all but the $600 refrigerators, we carry a cooler and drain it off now and then. The "house battery" runs a 200W Kenwood/Polk stereo system and special effects lighting and power supply/charging duties, etc. in the campsite.

 

I would probably buy a Harbor Freight solar kit that comes with a charge regulator and safety shutdowns to charge the battery. Only buy when on sale and sign up for their email coupons. Start with a charged battery at home, plug in the cooler directly when the car's running, and use the solar during the day to keep the charge on your camping battery.
If you absolutely have to, I might find an auto dc input charger for charging the battery. You have to keep the size down or you will overload the car's cigarette lighter outlets. Some examples are low power 50 w units like this one.

 

The 500W solar system you might want to recharge your battery will be bulky, over $500, and not practical unless you plan on long-term camping vs. 3 or 4 days that an AGM will provide without the big panels and charge controllers. Those "little" systems are really only useful to keep a system topped off, like during non-use. An off grid system will work better at around 750 v and take up about 1/4 the size of a 30' motorhome roof, and require at least two Optima batteries (as seen on Rock My RV with Bret Michaels). A single Optima will fit behind the seat, weigh only 42 pounds, and provide the refrigerator with 50 Ah per charge. Remember that whatever the Ah draw of the refrigerator, it will cycle on and off and that rating is for during on cycling.

 

Often overlooked check out mobility batteries for this sort of use. They are designed for regular deep discharge applications and come in capacities to suit most applications. The are sealed AGM batteries that can be used and charged in any position without leakage. Capacities run from around 20 AH to several hundred AH but 100 AH batteries can be bought for about the same price as an Optima 40 AH.

John (Britprius)

 

I agree with Britprius that the Optima, while good, may not be enough if you are not going to recharge as you go. Based on the Coleman's specs, you might get 13.3 hours of continuous use with the best Optima and much less from the Prius 12v without running the Prius and burning gas periodically. Perhaps with a 100 ah AGM you might get 2.5 times the runtime, or a day and a half. Obviously if the cooler cycled at 50/50 rate then you can double those times again to 26.6 hours and 3 days respectively.

Coleman recommends no more than 4 hours off a vehicle battery while not being charged to avoid battery damage and a possible no start.

 

Coleman fridges are the bottom of the barrel and you can get models up to $600 from quality manufacturers that use a lot less electricity (like the heat pump type rdgrimes owns). Even so, no refrigerator is going to run continuously. Britprius doesn't realize that Optima batteries ARE deep-discharge mobility batteries, and they are one of the best (aircraft approved, can be used upside down, etc.) you can buy IMO. I own an optima AGM and fabricated my own double-fused wiring with quick disconnect connections and heat-shrink covers. The Optima I own is the small one (55Ah), they make other models with more Ah. I paid around $120 at Costco using a coupon. There are other AGM battery companies and they are similar in technology. I wouldn't bother with an electric fridge (yes I do own one, similar to the Coleman) other than use on-the-road use due to their small size for the Ah draw, and a cooler with ice is a very inexpensive alternative. If money's no object, a heat-pump fridge and an AGM like the Optima are the way to go. Keep your AGM on a Shumacher float charger ($20, Walmart) when not in use for longest lifespan.

 

Thermoelectric heat-pump fridges are, for the most part, junk. They don't last due to condensation in the thermocouples and they are REALLY inefficient. Top that with nearly no insulation and they are really poor performers. Ice is way, WAY better in a good cooler.

I have disassembled several of failed TE units and even built my own- one was a multi-stage deep freeze down to -20F. HUGE power and water-cooling for that one, power was no issue in that case. But the truth is- it is hard to beat the efficiency of a good old fashioned QUALITY compressor-type fridge- for $$$. Look at the types used in boating- ridiculously expensive, but very efficient ! They have to deal with the same problem, limited battery and you don't want to run a boat engine or gas aux generator all the time. You will never see a thermoelectric fridge installed on a boat- never.

Not sure what the 12V charging capacity is in a Prius, but why waste gas charging while splitting what's available between two batteries? Ice is cheap, non-toxic and yes, it won't keep frozen stuff frozen, but it will keep cold stuff for a long time if a good insulated cooler. Save your Prius battery from premature failure and yourself from a long walk.

 

Mag_Gray-V5, have you seen the specs and owner reviews for the $600 models? These things, while way out of my budget for a cooler, are light-years away from the little $100 models (I have one and it's inefficient and poorly constructed). If price was no object, I would own one after reviewing them without cost as a consideration.