Introduction
Back in October 2025, Sharlene and I bought a lightly used 2022 Winnebago Solis 59P camper van! Sharlene had just left her job at Notion in order to spend time with me in the last few months of my sabbatical year, and we decided the most exciting way to spend our time would be to do an extended camper van trip.
We had a very memorable time traveling, first around the Southwest in late October through November and then hanging out along the Southern California coast in December. I think we grew a lot as a couple, while also having a lot of fun!
I may write separately in the future about our van travels, but this post is specifically just to document the electrical system upgrades I've made to the van so far.
I hope this is helpful for anyone considering similar modifications to their van! I've been really enjoying tinkering on the van and gradually making it work better for us.
Summary of changes
Going into our October–December big trip
- Replaced the two original lead-acid AGM house batteries with one 165 Ah lithium (LiFePO4) battery
- Replaced the original isolation solenoid with an Li-BIM 225 isolation module
- Bought a portable power station (Anker Solix C1000 Gen 2) to run our 120 V AC appliances
Additional changes after our big trip
- Replaced the shore power converter with a lithium-battery-compatible unit
- Wired in a dedicated charging cable for the Anker power station
- Replaced the original PWM solar charge controller with a Victron MPPT controller
The original system
When we bought the van, its electrical system was unchanged from the Winnebago original. Here's a diagram I made of that system:
This is a pretty typical RV electrical system. When you're connected to shore power, everything works, but when you're not connected to shore power and the engine is off, you can only run your 12-volt DC systems. The 120 V AC outlets in the van are energized only when the van is connected to shore power.
Our van doesn't have a generator since it's the 59P model. The 59PX model has a built-in gas generator which does power the 120 V AC outlets, but I didn't really want the generator due to noise and maintenance. (We also didn't care for the extra length or the A/C unit of the PX.)
Project goals
Off the bat, when we bought the van, the original house batteries were not holding a charge and needed replacement. (This type of lead-acid battery gets damaged if discharged too deeply, so for a used van, this was somewhat expected.)
We wanted to be able to run a microwave and Instant Pot to heat canned soup and cook rice, while also primarily camping off-grid without relying on shore power.
Many people want to run air conditioning off their batteries too, but for our travels this was not part of our wish list.
We didn't have a specific budget, but two new AGM batteries would have cost around $600-$1000, so we were aiming for a cost not too much greater than that.
Keeping it simple
Some other Solis owners have done extensive van upgrade projects that often involve adding many more lithium batteries, relocating batteries inside, and adding an inverter or combined inverter/charger/transfer switch unit. These projects are really neat because you can build a very integrated and capable system.
However, we wanted to avoid making major modifications to the van, because:
- We wanted to hit the road as soon as possible, rather than spend our precious days prepping the van
- We weren't sure if we might sell the van after this trip, and big modifications usually don't help resale value
- We weren't very familiar with the van's internals, so we didn't feel confident performing deep rocket surgery
1. Lithium (LiFePO4) house battery
The total usable capacity of the two original AGM batteries was about 100 Ah.[1] I replaced them with a single 165 Ah LiFePO4 battery. This battery cost around $500 and has a Bluetooth-enabled BMS for checking the status, as well as self-heating capability so it can be charged in cold temperatures. It's the same physical size (Group 31) as the original batteries.
Installation
With the help of my friend Corey and his transmission jack, removing the old batteries and putting in the new one was fairly straightforward. The two original batteries were mounted underneath the van, one in front of and one behind the rear axle. I put the new battery in the front mounting cage and removed the rear mounting cage. As a bonus, removing the rear battery freed up space to mount a spare tire underneath the van.[2]
After putting in this battery, I changed the Xantrex solar charge controller's battery type setting to the LiFePO4 option (very easy, just a few button presses per the manual).
As an extra safety measure, I also added a 200 A fuse at the positive terminal of the new battery. (I don't remember exactly which one I bought, but it was similar to this one on Amazon.)
Reflections on battery sizing
We did have to watch our battery carefully to avoid running out of energy, particularly when parked in one place for more than a couple of days. More solar power and/or a bigger battery would have helped with this; I believe the biggest battery that still fits in the stock Solis mounting cage is the Epoch 300 Ah battery. Having that much energy would've been very cool, but that battery also costs $1200, so ultimately I think the Li Time 165 Ah battery was a reasonable compromise for us.
Issues with state of charge accuracy
Our Li Time battery's reported state of charge (SOC) in the app was often very inaccurate. It turns out that the battery needs to be charged to 14.6 V in order to consider itself 100% charged and recalibrate its SOC number. The van's alternator, solar charger, and shore power converter could only get the battery to around 14.2 V, which is enough to get it to a 99% SOC but not to the magic 100%.
After this recalibration, the SOC is reasonable for a short period (maybe a few days, I'm not sure) before needing another 100% charge to calibrate again.
Unfortunately, I only figured out the cause after our big trip. During our trip, the battery sometimes shut itself off due to low cell voltage while the app still reported a reassuring SOC number (usually around 30%, but one time as high as 70%). And during discharge, it would stick at 99% for a long time before dropping later than expected, resulting in the high SOC estimate. After waking up to a dead battery a couple of times, we ended up just watching the voltage number closely and generally not trusting the battery very much.
I contacted Li Time support and the company shipped me a new battery under warranty. (Credit where it's due for the good support!) The new battery initially seemed OK but then started to exhibit the same behavior. It was only after I installed the new power converter (item #4 in this post) and charged the battery to 14.6 V that the inaccuracy went away.
2. Li-BIM 225 isolation module
The stock system has a solenoid that connects the house and chassis batteries whenever the van is running. Apparently this solenoid is a common point of failure, so other owners often replace it with a Precision Circuits Li-BIM 225 ($135). This device does much the same thing, but is supposedly more reliable and will also cycle the connection periodically as a way to try to keep the alternator from being overloaded for too long. It will also charge the chassis battery from the house battery when parked if the house battery has a high enough voltage.
Installation was fairly simple. I basically followed this video by Scott Griepentrog, except for the diode and boost switch modifications at the end.[3] After disconnecting both chassis and house batteries for safety, I opened the junction box under the van, removed the solenoid, moved the electrical connections over, and mounted the Li-BIM 225 using a couple of self-tapping sheet metal screws.
After we put in the Li-BIM 225, we noticed that the battery didn't seem to be charging from the alternator because the Li-BIM wasn't engaging. However, we also weren't sure if the battery had ever been charging properly before the Li-BIM installation. Eventually, we traced the issue to a relay behind the plastic interior trim of the passenger side B-pillar: one of the spade wire connectors to the relay was loose, and this was preventing the "engine on" signal to the Li-BIM. So, the issue was unrelated to the Li-BIM and not caused by it.
Reflections
I'm not sure the Li-BIM was really necessary because the Ram Promaster alternators don't actually seem to fail very often, especially when charging our relatively small size house battery. The behavior of the Li-BIM also made troubleshooting our charging and battery issues a little more complicated. But now that it's there, I'm happy to leave it and not worry about it.
3. Anker Solix C1000 Gen 2 portable power station
IMO, this is the easiest way to get 120 V AC power—much less involved than integrating an inverter into the van. The power station also increases our energy storage capacity.
After some research, I bought an Anker SOLIX C1000 Gen 2 for around $500. It has 1 kWh of energy capacity and can output 2 kW. This specific model has all its outputs on one of the long sides, perfect for our chosen placement behind the wet bath, where it won't fly forward when we brake hard.
It just sits in the cargo area of the van and charges off the house battery via the existing 12 V socket by the galley sink. I used some tape to manage the charging cable.
Reflections
I'm really happy with the Anker power station and am very glad I got it rather than trying to install an inverter. I've had zero issues with the Anker. We were able to microwave our soup and cook our rice! I really love the whole battery system and find it kind of unreasonably exciting and fun.
The only issue with this setup is that charging the Anker can kill the house battery, so we had to actively keep an eye on the batteries and unplug the cable if the house battery was getting low. I remedied this later with a low voltage cutoff in my hardwired charging cable (see #5 below).
Here's the system diagram again with these three changes highlighted in yellow:
4. Lithium-compatible shore power converter
After our big trip, I had some time to tinker with the van a bit more.
In order to charge the house battery to the desired 14.6 V, I went ahead and put in a power converter that had a selectable lithium battery charge profile. The original converter WFCO WF-8955PEC only has a lead-acid battery charging profile.
The power converter is located underneath the WFCO fuse / power distribution panel, behind the black plastic cover. After unscrewing the screw at the base, the converter slides out and its wires can be disconnected:
Then, the new converter can be simply swapped in:
The name-brand WFCO part is WF-8955-AD ("AD" stands for auto-detection of the battery type). The genuine part costs $381 at time of writing, but Amazon has many cheaper generic options. I chose this WAVLINK brand one which has a physical switch to select the charging profile and cost $77 including tax.
Reflections
The new converter successfully charges the battery to 14.6 V and brings the reported SOC to 100%. After reaching 100%, the battery SOC recalibrates and seems to behave accurately for a short while (maybe a few days, I'm not sure) before getting wonky again.
In writing this post, I realized that I could have skipped installing this converter and saved my $77. The MPPT solar charger I later put in (item #6 below) is also able to get the battery to 14.6 V, so it achieves the same goal. We get solar all the time, but don't plug into shore power very often, so this converter will rarely get used.
Oh well, I guess. If nothing else, I learned a bit more about the van's electrical distribution panel.
Here's the system diagram with the new converter highlighted:
5. Hardwired charging for the Anker power station
During our big trip, we charged the Anker power station by simply plugging it into one of the van's 12 V sockets using the XT60 car charger cable that came in the box. This was easy to set up, but had a few limitations:
- Charging the Anker could completely deplete the house battery, leaving us without the ability to turn on our lights, use our furnace, or run our water pump. So we had to make sure to unplug the charger if the house battery was low on charge.
- The charge rate was limited to about 10 A (~120 W).
- The actual power getting to the Anker power station was only around 90 W because of the resistance in the small 12 V wires. About 25% of the energy coming from the house battery was being wasted as heat in the wiring! I was also a little nervous about potential fire risk due to heat buildup if there were any frayed wires, bad connections, etc. in the wiring.
First, I found this low voltage cutoff module on Amazon and bought it for $25.[4] This module disconnects a load from the battery when the battery voltage drops below a selectable voltage, and reconnects the load to the battery when the voltage rises again.
The voltage threshold is set using these DIP switches on the side:
At this 12.1 V cutoff threshold, the house battery should have around 10% charge left. In retrospect, I would have liked a higher threshold to keep more energy in the house battery, but this is much better than nothing.
I then wired the module into the one empty circuit available in the van's WFCO distribution panel using 10 AWG cable:
The specific cable I used was this one that terminates in a female XT60 connector. ($9). I removed the ring terminals to wire it into the distribution panel. I wasn't able to find an easily accessible negative busbar, so I did the slightly janky thing and just squeezed the negative end into the terminal where the power converter was also connected (the green wire at the right side in the photo above).
I then added this XT60 to XT60i adapter cable ($10) to connect to the Anker power station. The XT60i connector is the same as the XT60, except that it has an extra middle conductor which is tied to the negative wire. The presence of this conductor tells the power station that it is connected to a solar panel, rather than a car socket, and can safely draw 15 A instead of 8 or 10 A. For my setup, this is both safe (because the current is traveling through a short distance of thicker gauge cable) and desirable (so the Anker can charge more quickly).
Now, the Anker power station can charge 2x faster than before, at a whole 15 A (~185 W), without wasting a big chunk of power as heat!
I haven't had a chance to test the low voltage cutoff yet, but I'm optimistic it'll save the house battery from being wiped out by the Anker.
6. MPPT solar controller
Finally, I replaced the stock Xantrex PWM-type solar charge controller with a Victron SmartSolar MPPT 100/30 controller ($120 via Amazon).[5]
PWM vs. MPPT
Initially, I wasn't sure if this upgrade was worth doing. People on the internet agree that MPPT (maximum power point tracking) solar charge controllers are more efficient, especially in partially shaded conditions, but some people say it's minimal benefit in sunny climates for small panels like the 220 W one on the Solis, while other say it's very significant.
I found this technical document from Victron (PDF) to be extremely helpful in understanding the difference between how PWM and MPPT controllers operate.
Basically, PWM controllers simply connect the panel directly to the battery, so that the panel operates at whatever voltage the battery is at. The panel can work at this voltage, but it has its own maximum power point at which it generates the most power. For the 220 W panel on the Solis (datasheet PDF here), that point is at 25.8 V and 8.54 A under the standard test condition. So when our PWM controller connects the panel to the ~13 V battery, the panel is forced to operate far from its optimal voltage.
In contrast, an MPPT controller figures out what voltage the solar panel likes, draws power from the panel at that voltage, then transforms the power to a voltage appropriate for the battery.
After looking at the Solis panel's datasheet and realizing how far the maximum power voltage (Vmp) is from the battery's ~13 V, I started to feel that there were probably big gains in solar power available by switching to MPPT. I'd always been pretty disappointed in the solar output, and often wished for more battery capacity (as mentioned earlier). The MPPT controller is a lot cheaper and easier than buying more batteries, so I figured it was worth a shot.
Installation
Installation basically consists of carefully swapping the cables from the old unit to the new one, then mounting the new unit and covering the hole in the wall. For moving the cables over, I followed this order of operations:
- Disconnect one of the PV cables from the old unit. Cover with tape to prevent accidental shorting.
- Move the battery cables from the old unit to the new unit. Be careful not to short anything, and also be careful not to reverse the + and -, as the Victron SmartSolar isn't protected against reverse polarity of the battery! Green is - and black is + in my van.
- Move the PV cables from the old unit to the new one.
I mounted the SmartSolar unit to the existing plywood inside the Solis wall using some #6 x 3/4" screws and washers. #8 might have been more appropriate but I didn't have those on hand. No pilot holes were needed, nor could I have gotten a drill into the space to make pilot holes; I just used a screwdriver and it worked fine.
I then covered up the hole with an IKEA-Skadis-compatible pegboard that I 3D printed (STL here):
Reflections
The MPPT controller was a really worthwhile upgrade, and I wish I'd done it way sooner. I don't recall ever seeing the Xantrex PWM controller output more than 6 A (~80 W) on the sunniest winter days. In contrast, immediately after installation the Victron was outputting a consistent 160 W on a partly cloudy day—that's double the power in less optimal conditions! It feels like I'm getting so much free energy now.
Additionally, the Victron can be set to charge to the full 14.6 V that my house battery needs to calibrate its SOC. The Xantrex would cut off power before reaching 14.6 V.
The data available in the app over Bluetooth is also pretty fun to look at.
I haven't had a chance yet to take the van out on a trip and really test the solar controller, but just looking at the output, I'm already very happy with it.
Here's the final system diagram with those last two changes highlighted:
Conclusions
Overall, these upgrades make the van work a lot better for our needs, without fundamentally changing the architecture or operation of the van's electrical system.
If you're just getting started, and have similar needs/wants, I think I'd primarily recommend replacing the AGM house batteries with one lithium battery, and throwing in a portable power station to run appliances. Those two changes will enable a lot!
Then, put in the Victron MPPT solar charge controller to replenish the batteries faster when parked and get the batteries to 100% for more accurate SOC readings.
I would also recommend the hardwired charging cable for the portable power station.
The Li-BIM is nice to have, but not necessary. Finally, the upgraded shore power converter wasn't actually necessary at all for us.
I'm generally pretty happy with the choices I made and hope that this writeup is helpful for people researching similar upgrades for their vans. I find all this off-grid power stuff really fun and rewarding and am really glad to have had the opportunity to mess around like this with our van. Me and Sharlene's lives have been very busy lately (wedding planning!!), but we hope to take the van out for many more camping trips later this year! 🚐
Resources
- The Winnebago Solis Owners and Wannabees Facebook group has a lot of great information and owner experience.
- Scott Griepentrog at stg.net has a wealth of information on lithium battery systems and the Li-BIM for the Winnebago Travato and Solis. In particular, he has a huge Google Doc which provides lots of detail for DIYers.
Each battery had a nominal capacity of 100 Ah, but discharging below around 50% is not good for the batteries, so the actual usable capacity was about 50 Ah per battery. ↩︎
I think undermounting the spare tire is a lot better than the more common mounting on the rear doors. The mounting hardware is a few hundred dollars cheaper, you don't have to drill new holes into the van, and you can still open the rear doors the full 270º. My new spare wheel and tire cost $400 from Tire Rack. ↩︎
I opted to leave the "Sig" input disconnected to simplify installation. This input allows you to command the Li-BIM to connect the chassis and house batteries (e.g., if your chassis battery is dead and you want to charge it from the house battery), but getting it to work with the existing boost switch in the dashboard of the Solis requires adding a diode. I decided not to bother because it didn't seem worth the effort, and in case I wanted to swap back to the original solenoid later. The boost switch isn't really needed anyways because the Li-BIM will occasionally charge the chassis battery if the house battery voltage is high enough. ↩︎
I picked this particular model because it has a nice plastic enclosure and simple settings. There were some other products on Amazon that are cheaper, but they were unenclosed boards and had a more fiddly user interface. ↩︎
There are other MPPT controllers on the market, but Victron is consistently most recommended for quality and brand reputation. One person in the Facebook group recommends the $70 HQST 20 A MPPT controller on the basis that a 30 A controller isn't necessary; this seems reasonable to me, but I thought it was worth paying $40-50 more to have the better brand and support. If you want a flush mount unit to avoid having a hole in the wall to cover up, you could put in the Blue Sky Energy Solar Boost 3000i or the Rich Solar MPPT 30 A controller. However, both of these are a lot more expensive than the Victron, and I also think the Blue Sky Energy controller is extra ugly. ↩︎