The lithium Iron Phosphate (LiFePO4) battery has revolutionized the way we camp and power our campers, especially for those who like to boondock. Not only does the lithium battery provide a much higher usable capacity (90 percent) compared to the lead acid battery (50 percent), but it also weighs less, charges faster, and lasts longer. Unfortunately, the lithium battery suffers from one con that must be addressed in any RV used during the winter—the inability to be charged in freezing temperatures. Indeed, charging a lithium battery below 32 degrees will cause irreparable damage to the battery (a lithium battery can safely be used below 32 degrees, just not charged below that temperature). Fortunately, many lithium battery monitoring systems have built in thermal safeguards to shut down charging to prevent damage, but a way to “warm up” the battery in cold weather is still needed. This article explains how to build a simple lithium battery heating system for your RV for less than $100.
For this modification, you’ll need the following components available mostly through our friends at Expion360 who designed and tested this system for their excellent VPR PowerMod 12 volt Lithium Battery:
- One Battery Heater Switch (Part No. EV-V120-BHS $8.00 ea. Retail plus shipping).
- One or more Facon 7.25-inch x 25-inch RV Water Holding Tank Heater Pads available through Amazon.com.
- One or more optional Lithium Battery Thermal Wraps (Part No. EV-V120-TW $78.00 ea. retail plus shipping).
Note: Expion360 will be incorporating a thermal cutoff switch in their generation 2 VPR PowerMod batteries, which will be available in the spring of 2020. The low temperature shutoff, according to Expion360, will be a feature of the battery management system and will prevent charging below 32 degrees F and discharging below minus 4 degrees F.
The Facon Water Tank Heating Pad is the key component in this truck camper mod. The pad was engineered originally to prevent RV water tanks from freezing during winter, but works just as well on lithium batteries inside or outside the camper. We used two heating pads, one for each battery, in the Truck Camper Adventure Rig. Each heating pad comes with a 12 volt fuse and a self adhesive strip. The pad is long enough to cover the back and two sides of an Expion360 Viper Group-24 battery (if applicable, leave the front removable BMS panel accessible for maintenance). If needed, the rubber heating pad can be shortened an inch or two using scissors, but care must be taken not to cut the 12 volt wires extending into the pad itself.
If the lithium batteries are installed inside your RV, the battery thermal wraps will not needed (assuming, of course, you keep the temperature in your RV high enough to prevent freezing). If the thermal wraps are needed in your application, wrap each battery after the heating pads are applied to the batteries. Note: Expion360’s bus bars cannot be used with Expion360’s thermal wraps due to the narrow, 1/8-inch distance between the batteries when connected in parallel.
After the thermal wraps are in place, wire each heating pad to the main fuse panel or directly to the lithium battery using the included 10 amp fuse (we installed ours directly to the batteries using positive and negative bus bars). Lastly, install the master control switch to allow on-off operation of the heating pads.
Allow the heater to pre-warm the lithium battery for two hours prior to charging. Note: the battery heaters will draw 6 amps each during operation. Even though the heating pads have a built-in thermal switch, leaving them on constantly isn’t a realistic option with a 6 amp consumption for each pad. Make sure you have enough amp hours available in the battery to pre-heat and to keep the batteries warm during charging. Do not charge the batteries using the heating elements below the temperature of 0 degrees Fahrenheit.