I have finished the LiFePO4 battery
installation in our Lil Snoozy
. We used the Li battery boondocking
for 4 days a few weeks ago but I finally hard wired in all the pieces, including the ability to charge while driving, yesterday. I am no expert in batteries and chargers, I am a geologist. So I may have done something really stupid in my installation. I am only describing what I did. Please do your own research and make your own decisions. Please let me know if you have ideas for improvement.
Putting in a single Battle Born 100 Ah battery
ended up not being a drop-in installation. It did eliminate the need for a battery management system, which made the installation much easier. If you mainly camp in RV parks and can plug in every night, you can just drop in the BB Li battery and be fine (but then you don't need a Li battery) but if you boondock, you need to make some changes. Only the charger wiring is absolutely necessary but you will significantly limit the benefits of Li batteries if you don’t do the others. Why buy an expensive, high performance battery and then handicap it?
The changes I made are:
Replace the stock WFCO 9835 35 amp charger/converter with one that is designed for Li batteries. A Li charger will charge at higher voltage and higher amperage and doesn’t have features designed just for lead acid. The WFCO won't charge the Li battery unless the voltage drops pretty low (see initial post in this thread). So this change is not entirely mandatory, but pretty close. One of the advantages of Li is high-amp charging so you can fully recharge in an hour or two off of shore or generator
power instead of many hours for lead acid. I installed a Progressive Dynamics 60 amp lithium charger purchased from Battle Born. The Progressive Dynamics charger/converter charges at 14.6 volts, but the BB Li battery is regulated against overcharge at 14.4 volts, so no problem there. When I charged a 90% full battery with the new charger and wiring, it charged at 55 amps, as designed. Another advantage of the PD charger is that the fan doesn't come on all the time like the WFCO, and when it does, it is really quiet.
Replace the stock 12 gauge charger/converter wiring with 6 gauge so you can charge at up to 60 amps. This is a big deal. If you keep the WFCO 9835 and try to charge a depleted LiFePO4 battery with it, it will charge at close to 35 amps, which far exceeds the ampacity of the 12 gauge wiring supplied with the Snoozy. It is even worse with the Progressive Dynamics 60 amp charger I installed. So you must replace this wiring.
Build a new battery rack. You don't need the big, plastic battery box because the LiFePO4 battery is solid state and not lead acid. That frees up a ton of room and you can easily fit two BB Li batteries between the hot water heater and the hatch door.
Install a 300 amp fuse on the battery because it has the ability to discharge to a short at a much higher rate than the stock AMG battery.
I installed a Victron battery monitor (BMV 700) with dongle so I can keep track of charge level, amp-hours used, and charge/discharge rates. This is not essential but it is really hard to track battery status doing it manually with a multimeter. There is a video on the Battle Born website on how to program the monitor for their battery.
My 4Runner has a factory isolator that keeps the trailer from draining the vehicle starter battery in camp with the engine off. If you don't have that, you will have to install one, or unplug the trailer wiring harness in camp. This is a potential issue with either lead acid or Li batteries, but the next paragraph describes a much better solution to a battery isolator alone, that is needed for the Li battery.
To charge the Li battery while driving, you need to install an isolated DC/DC converter between the tow vehicle and the battery. I use a 7-pin tow connector so that the vehicle will charge the battery and run the Truck Fridge
while driving. It is optimum to arrive at camp with a cold fridge
and charged battery. The stock trailer AMG battery setup works okay because the vehicle and trailer batteries are both lead acid. But the Li battery has a higher voltage at full charge so it won't charge from the vehicle without a modification. While driving, a fully charged trailer Li battery will actually discharge to the vehicle lead acid battery. To prevent this and charge the trailer Li batteryn instead, the DC/DC converter takes alternator current at, say, 13 volts and bumps it up to 14 volts or so, enough higher to charge the Li battery. Putting the DC/DC converter near the trailer battery also takes care of the voltage drop from the alternator over ~30-40 feet of 12 gauge wire to the trailer battery, which is probably about 1 volt. I got a Victron DC/DC converter (Victron Orion-TR 12/12-9) and set it to charge at 14.2 volts, although it can be set to charge higher. Since it is isolated, it also prevents discharge from the trailer to the tow vehicle. When charging a 90% charged battery it was running at 8.5 amps, plenty for a fast recharge.
Finally, I installed a battery cut-off switch that I can use to isolate the battery for storage or in case of a short somewhere. This is something I would install regardless of battery type.
How has it worked? I didn’t have the DC/DC converter installed when we went camping so we went more than a day without charging on the trip down. There was plenty of power to run the fridge
, and water pump for over a day. The stock AMG would have been nearly depleted. I used my generator
for 30 minutes one day and I vampired off of my neighbor’s generator
for 45 minutes another day. I got plenty of juice and returned home with about 70% charge remaining. We head out for a 5-day trip this weekend and I will report back afterwards.