Second battery wiring question

PeterTAB

Hi everyone,

Background:
I have a 2024 TAB 400 that came with a 100Ah Battleborn lithium battery and 310W solar panel.

Dry camping this past weekend, our battery capacity would drop to around 60Ah right before dawn from using lights, running the fridge, running the sound system for an hour or two, keeping the Alde on all evening and night, and running a white noise machine at night.

Our campsite had plenty of sun exposure so we were back at 100Ah by around noon.

I would like to be less reliant on solar for cloudy, winter days in a heavily forested campground so I want to double our battery capacity, which should be enough for 2-3 night camping trips without worry.

I considered getting another identical 100Ah Battleborn and wire it in parallel, but it would set me back about $1000 so the biggest downside is cost here, but can't beat the simplicity and ease-of-use.

I also considered an EcoFlow River 2 Pro power station, which has 64Ah of capacity and is currently on sale at Costco for $400. However, this is really only maybe 50Ah of usable capacity once you consider the inefficiencies of going through an inverter and a converter to power all the 12V stuff. Also, I don't like the idea of leaving it outside where the short power connector is, or just lugging it around in general, and wasn't sure how well it would be able to charge the Battleborn directly over DC if I wanted to address the inverter-converter inefficiencies (I might have needed a separate DC-to-DC charger, which probably has its own losses?)

Then I found a post by @CrabTab on this thread: https://tab-rv.vanillacommunity.com/discussion/14199/solar-generator/p1 where they suggest just getting a 2nd, possibly cheaper battery and using a battery isolation switch to activate it. I really liked this idea as it's quite economical and possibly provides the highest Ah per dollar, without being too inconvenient 

So I ordered a LiTime 100Ah battery for $252 and a battery isolation switch for $40.

https://www.amazon.com/dp/B084DB36KW (there was a lightning sale yesterday)
https://www.amazon.com/dp/B000K2MCR2

Actual question:

Here's a picture of the battery bay. I plan to put the new LiTime battery directly below the existing Battleborn. I've added little numbers to all of the positive writes coming out of the positive terminal. When adding the battery isolation switch, which of these wires do I need to move over to the switch so that they can be energized by either battery, and which of them should be left on the Battleborn battery?

My current understanding is:
1. This is the main wire powering the trailer and charging the battery, so this needs to be moved to the battery isolation switch.
2. This is the power for the Victron shunt. It doesn't matter where this one goes since the power draw is so minimal I could just leave it on the Battleborn even when it's disconnected from the battery isolation switch.
3. No idea what this wire is. It has a fuse. Does anyone know?
4. No idea what this one is either. I bet I could figure it out if I took off the panel on the left, just haven't had a chance yet...
5. Battery heater. This should stay on the Battleborn. There's no heater on the LiTime so there's no point in moving this one over.

Thanks!

kevmon

The fused wired is for the 12 volt dc side of your electric, I think. That’s what it was on my 320 but no inverter, so I may be wrong. The other unidentified wire is maybe from solar charger? It is hard to see. I assume a minus wire is also on shunt load from solar. This factory wiring is a mess. 

I have no idea why they put so much on the terminals. With exception of battery heater wire, BB recommends no more than two connections on each post—one on each side of each terminal.
Bus bars would make this so much cleaner. 

I would use bus bars. Positive to inverter, DC, and solar controller all on a bus bar positive following isolator. All minus to minus bus bar. Others more knowledgeable can chime in, but that’s my first guess. 

The shunt will only work with one battery system, so it will not work with your new battery, if I understand correctly. There is also the issue with solar charging for the different batteries. I suspect you will have two profiles in your victory app depending on which is being charged. Make sure you use appropriate wire size from battery.

elbolillo

 My thought is that you should have ordered 2 of the LiTime batteries and installed them in your 400. Then sell the BB.

I think you are adding too much complexity to your system and points of failure. Plus, you will be making it more difficult for monitoring the batteries and charging via solar.

PeterTAB

kevmon said:

The fused wired is for the 12 volt dc side of your electric, I think. That’s what it was on my 320 but no inverter, so I may be wrong. The other unidentified wire is maybe from solar charger? It is hard to see. I assume a minus wire is also on shunt load from solar. This factory wiring is a mess. 

Thanks @kevmon, so it must be that #1 goes to the inverter (makes sense given its size), #3 powers the 12V stuff in the trailer (makes sense given the fuse), #4 goes to the solar charger.

kevmon said:

The shunt will only work with one battery system, so it will not work with your new battery, if I understand correctly.

Hmm I was thinking that if I connected the shunt to both batteries and configured it via the Victron app that it's a 200 Ah battery, what I would see is that when the Batttleborn is 90% depleted the app would show me I have 110 Ah left. So I would flip the switch to activate the LiTime battery at that point.

Then when the app shows 20 Ah left, that would be the point when the LiTime battery is also 90% depleted.

Same goes for charging the batteries back up again -- when the app shows 110 Ah or 0A being pumped into it means one of the batteries is full and it's time to flip the switch.

kevmon said:

There is also the issue with solar charging for the different batteries. I suspect you will have two profiles in your victory app depending on which is being charged.

Hmm I hadn't thought of this -- I figured that since they're both LiFEPO4 that they would have the same charging profile, but let me look into this further...

kevmon said:

Make sure you use appropriate wire size from battery.

Acknowledged, I have 4 AWG cables and I should only need about a 12" length.

elbolillo said:

 My thought is that you should have ordered 2 of the LiTime batteries and installed them in your 400. Then sell the BB.

I think you are adding too much complexity to your system and points of failure. Plus, you will be making it more difficult for monitoring the batteries and charging via solar.

@elbolillo heh as I was typing the above I was definitely thinking "man elbolillo is totally right, this is pretty complex". But the Battleborn battery is just so much better built than any other battery that I can't bring myself to sell it. It's irrational, I know -- if I had a trailer with no battery and $1000 in cash, I definitely would not drop it on a Battleborn. But now that I already have one, I don't want to sell it Consider it insurance in case the LiTime craps out.

elbolillo

@peterTAB I don't think you can hook both the batteries to the smart shunt and have it monitor them as if it was a single battery. You are able to connect the smart shunt to a second battery in order to monitor it via the aux port.

pthomas745

In the "Anyone Carry A Spare Battery Thread" there are many different ways to add extra battery resources without any major rewiring.  Your Ecoflow can be wired directly into the 12V setup in the trailer and run the trailer 12V items.  An extra battery can be attached to a "12V plug adapter" and run the trailer.  An extra battery can be plugged into a 12V port and run the trailer.  See the "Anyone Carry a Spare Battery" thread.

https://tab-rv.vanillacommunity.com/discussion/7008/anyone-carry-a-spare-battery/p1

When I've used the 12V adapters or the 12V cable into a 12V port, I turned the battery switch off, so only one battery was used to work the trailer.

Several owners of the "batteries in a box" have used the 12V regulated output to a 12V port for running the trailer.  There are limitations on the amount of wattage you could ask from the battery and the 12V port, but for basically running the trailer overnight, it should work fine. 

kevmon

elbolillo said:

 My thought is that you should have ordered 2 of the LiTime batteries and installed them in your 400. Then sell the BB.

I think you are adding too much complexity to your system and points of failure. Plus, you will be making it more difficult for monitoring the batteries and charging via solar.

I agree with this 100%. Two identical batteries make this easy all the way around.  They work as one for monitoring, charging and discharging. 

PeterTAB

All done. Seems to work exactly as I had hoped. The solar is able to charge either battery (they have the same charging profile -- 14.4V absorption / 13.6V float). Same goes for the converter. The shunt thinks there's a single 200Ah battery. When it gets down to 110Ah / 55% (or I otherwise expect it to hit 100Ah/50% over night) I'd flip the switch.

Some things I learned / noticed:

1. Victron recommends connecting the battery before enabling solar charging. If I switch from Battery 1 to Battery 2, it momentarily goes through the "off" position which may not be great. I need to remember to turn off the solar charging through the Victron app before turning the switch.

2. The solar charge controller came from the factory with a float voltage programmed to 13.8V which I think is too high. Both Battleborn and LiTime recommend float voltages of 13.6V.

3. I'm still not sure what wires #3 and #4 are. It seemed to me while I was testing the various wires that both the 12V power in the trailer and the solar charging are supplied through wire #1.

pthomas745

We have pictures of other trailers with the battery fuse in the vicinity of the battery disconnect switch (I'm thinking of your wire #3).  On those trailers, the solar cables were routed to the battery distribution block, so you might want to follow the wires from the block, or follow #3 to where ever it goes out the space under the Stinger inverter fuse.   

ScottG

PeterTAB said:

...
1. Victron recommends connecting the battery before enabling solar charging. If I switch from Battery 1 to Battery 2, it momentarily goes through the "off" position which may not be great. I need to remember to turn off the solar charging through the Victron app before turning the switch.

...

@PeterTAB, I have the same switch. You can prevent disconnecting the power while switching if you go through the "1+2" position rather than the "Off" position. You will be momentarily running both batteries in parallel, but the connection will remeain uninterrupted.

Of course, this setting also gives you the option of running the two batteries in parallel, in the event that you ever wanted to do so. 

PeterTAB

Thanks, good point that it's probably fine to run them in parallel for a quick second while switching batteries. EDIT: see below; probably not fine if the state-of-charge is very different between the two batteries.

Is there ever a reason one might want to run them in parallel for an extended period, given they're from two different manufacturers?

ScottG

PeterTAB said:

...
Is there ever a reason one might want to run them in parallel for an extended period, given they're from two different manufacturers?

Not that I can think of, but down the road you might have matched batteries, so at least you have the option.

My understanding is that even running unmatched batteries in parallel--while not optimal--is not the end of the world. The batteries will try to equalize each other if their states of charge are different, but they will still work.

(Somebody feel free to set me straight if I'm fundamentally wrong about this!)

PeterTAB

I spent some time reading about this and it sounds like the main consideration with connecting 2 LiFeP04 batteries in parallel is to ensure they're at the same voltage first to avoid large currents with one battery trying to charge the other. It generally seems recommended to charge both to 100%, let them both sit for a few hours, check voltage on both to make sure they're the same, then connect them in parallel.

Should be fine even if they're from different manufacturers, but some people suggest you might decrease their service life slightly from extra charge/discharge cycles as they try to match each other's voltage.

That does mean that it's probably not a good idea to flip the switch to 1+2 in the middle of a trip when the two batteries are likely at different voltages.

kevmon

I would be careful running two batteries in parallel if one is fully charged and the other discharged. As stated above, the full battery will try to pump power to the depleted one. 

I am happy to be corrected, but my understanding is that this could be a lot of current running through relatively small wire. Perhaps more than 4AWG can handle. I use 2/0 wire between my batteries and would not attempt this. I suspect most modern BMS would protect batteries, but more knowledgeable folks can chime in to correct me. 

SLJ

This is not how it should have been done.
Mismatched batteries is a problem. Worse, having batteries at different charge states is a real problem as there can be a huge amount of current created if a charged battery and a discharged battery are connected together. Batteries of the same manufacture/model should have been used and both should be fully charged individually and then connected in parallel and allowed to balance. Having two batteries in different charge states on a switch that will allow them to even momentarily be connected together in parallel means your depending on the batteries BMS to limit the current between them or shut them down. Dumping a lot of current from one battery to the other can create a lot of heat and lead to disaster.

PeterTAB

Agreed, I don't plan on connecting them together even for a moment. The switch allows for going through the "off" position when going from battery 1 to battery 2.

ScottG

The concern about a large current dump between the batteries seems valid if there is a big difference in voltage when making the switch. But now I'm curious... does anyone know how much current we're talking about, or--better yet--how to calculate it based on circumstances?

PeterTAB

My layman's guess would be that it would be something like the voltage difference / the internal resistance of the two batteries.

Might be as high as 2V / 10 mOhm = 200A?