Sanity Check - RV Battery

I have an RV on order, a small class C/B+ (LTV WRL-AWD), and I want to put in an electrical system for off grid camping without relying on a generator. Nations has a second alternator kit for the transit with 280 and 370 amp 12v alternators. I contacted them about higher voltages and was told they're working on 100 and 120a 48v alternators, fitting them to their test vehicle now. So that's great, and the Magnum MS4048 inverter looks good to me. Enough power to run 2 high draw appliances with a bit left over, good charging capacity, compact although heavy. The surge capacity isn't great, it can barely start the A/C which means if something else is on it might overload the inverter. But there are ways around that.

So that's all great, but it leaves the batteries. I've been looking at Lithionics, and Battleborns, and off brand stuff Will reviews like the Ampere times. They all take up a lot of space, they're expensive, and they usually fit really awkwardly in the RV compartments, leaving a bunch of wasted space. It is not a floorplan with good storage. So now I'm thinking of using the Lishen cells from varicore. 4x4 sets of them for 16 cells, connect them all in series for one 48v unit, get a single 16s BMS. I'm not sure which BMS, needs at least 150A since I want to get the bigger alternator.

My questions is, this all seems too easy and too cheap for so much benefit. I can fit 13kwh of batteries and a 4kw inverter in the space the manufacturer has 2 batteries and a 2000w xantrex, all for $2k (for the battery)? And it looks dead simple to build, at least for an engineer. I was watching an old video of Wills and he comments this is basically arts and crafts and I agree. Am I missing some factor here that makes this more expensive or more difficult than it looks, or should I get those cells on order?

I'll add solar panels eventually but they're just to extend camping time and keep the batteries charged, you can't mount enough on an RV that size to charge that battery in a reasonable amount of time.

Welcome to the forum.

What's your actual need? One sizes a system and select components based on their needs. I'm not seeing that.

Consider also that using the vehicle exclusively as a generator is horrifyingly inefficient.

snoobler said:

Welcome to the forum.

What's your actual need? One sizes a system and select components based on their needs. I'm not seeing that.

Consider also that using the vehicle exclusively as a generator is horrifyingly inefficient.

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That's hard to say since I don't have the RV yet, and it's going to vary enormously depending on the weather. IE air conditioner use. But for a 48V system you need 16 cells, and I'm pretty sure that will exceed my need. I also suspect I won't need to run the engine much to charge, unless it's hot out it will probably take days to run that battery down.

So plan 1 was to not buy any electrical components to start, go out and experiment with the RV and see how much electricity I use. But that's a bit tough if I don't have a generator, and if the battery cells take 2-3 months to deliver...

That inverter has a surge of 8500 watts. What kind of AC are you running?

Disclaimer: Peoples feelings seem to get hurt really easily around here so I just want to be clear, this is a personal opinion, everyone is free and clear to do what ever you feel is right for you and I am not cutting down anything you want to do as I dont know and have no interest in understanding fully what your personal situation is. Im just throwing out and idea you may not have known about.

I do not and have no intention of using solar (for now). For me I did not want to rely on having to run a vehicle engine and fitting a second alternator for the intended purposed of charging batteries isnt cheap either. I suggest you you look at finding an inverter that has the ability to limit shore power current (like the multiplus) so that you can forget about alternator charging ( maybe stick a DC-DC if your heart is set on that and just charge at a slow rate when you are actually driving) and instead buy 1000 generator that can chug away in the distance putting out 750w when your batteries are getting low.

This is what I am doing.

noenegdod said:

That inverter has a surge of 8500 watts. What kind of AC are you running?

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It comes with a Dometic Penguin II. Dometic lists the locked rotor current on their web page. I forget the number but if you multiply it out it comes to about 8000w. Other 4000w inverters often have a 12000w surge, but the Magnum has the best charger for charging the battery off shore power or a generator. Also it's more cubical, hard to fit in a 20+ inch long inverter.

A portable gen instead of the 4000W onan you can get built in is an option. A DC-DC would take forever to charge the batteries. I'm not sure how much you're allowed to pull off the primary alternator, but it only comes with a 30A 12v one, so 360w.

Mobile applications are more challenging for a diy battery.
The big blue prismatic cells usually have m6 tapped aluminum terminals that tend to strip.
The terminals themselves are also a bit dainty as in care must be taken so they don't get ripped out of the cell.
Finally the whole cell is just a thin aluminum can.
I have an idea to leave the cells in the foam they are shipped in and use wire instead of busbars for the interconnects.
Not sure if the foam tolerates heat well enough though.

smoothJoey said:

Mobile applications are more challenging for a diy battery.
The big blue prismatic cells usually have m6 tapped aluminum terminals that tend to strip.
The terminals themselves are also a bit dainty as in care must be taken so they don't get ripped out of the

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I was mostly asking about the electrical aspect, but building the battery to minimize rattling and vibration is something I'll consider.

Toddmccollam said:

It comes with a Dometic Penguin II. Dometic lists the locked rotor current on their web page. I forget the number but if you multiply it out it comes to about 8000w. Other 4000w inverters often have a 12000w surge, but the Magnum has the best charger for charging the battery off shore power or a generator. Also it's more cubical, hard to fit in a 20+ inch long inverter.

A portable gen instead of the 4000W onan you can get built in is an option. A DC-DC would take forever to charge the batteries. I'm not sure how much you're allowed to pull off the primary alternator, but it only comes with a 30A 12v one, so 360w.

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Absolutly, DC-DC isnt a way to actually charge the batteries from depleted if you actually need power. Its just to trickle in a little power since you are driving anyway but it does not sound like that is really an option with the factory alternator.

I suggest this because most people think that they need a generator large enough to start AC or other big loads and they need a generator that can output enough power to satisfy the charger they have. This isnt the case. You can actually have a tiny 1000w generator that will look after all your power needs for the day and the batteries\inverter simply act as a buffer to store and release power as required all the while you are trickling in power through the day.

If you actually need 8000 watt surge the multiplus wont work for you though. Its surge is only 6000w combined with the little generator limited to 750W your only at 6750W.

Good luck!

noenegdod said:

Absolutly, DC-DC isnt a way to actually charge the batteries from depleted if you actually need power. Its just to trickle in a little power since you are driving anyway but it does not sound like that is really an option with the factory alternator.

I suggest this because most people think that they need a generator large enough to start AC or other big loads and they need a generator that can output enough power to satisfy the charger they have. This isnt the case. You can actually have a tiny 1000w generator that will look after all your power needs for the day and the batteries\inverter simply act as a buffer to store and release power as required all the while you are trickling in power through the day.

If you actually need 8000 watt surge the multiplus wont work for you though. Its surge is only 6000w combined with the little generator limited to 750W your only at 6750W.

Good luck!

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There's something called a soft start you can put on the AC which slows down the rotor startup time. We're talking 1/6s to about 1/2s, so not something noticeable to a user. It costs $300 and brings the surge down to...I forget, but you can run the AC on a 2000W inverter at that point. It sounds too good to be true but there are plenty of videos on them, I even found one where an electrical engineer had that exact A/C hooked up to an oscilloscope showing what the soft start can do. And coleman now includes the soft start in some of their A/Cs, so it's a real thing. My point being, the A/C surge shouldn't be a deal breaker.

The 4000W inverter generator the RV comes with is made to run the electric system directly. So yes, with a battery powered RV I wouldn't need that, just something that could charge the batteries. But I like the alternator because it could charge the batteries fast, that 120a 48v one is putting out 6000w. The transit can actually be optioned with a second alternator from the factory (tho it's 12v and only with the ambulance package), so adding it isn't a crazy idea. There's basically a spot designed in for it.

If by multiplus you mean the victron inverter it's too big and not available in the power configuration I want.

Edit-I type too slow....

Don't worry about ordering batteries for a bit-today is New Years day-not a lot of work going on.
I don't think you are missing much in your thoughts, it can be that inexpensive for the benefit. You may want to think about the price of the cells-don't necessarily go for the cheapest, look in the forum for group buys.
It's really hard to say how much power you will need, depends heavily on what you are using, A/C is really hard on power. With a soft start device you could probably run it with the Xantrex (if it's pure sine). What other loads does the RV have? I do like that Magnum.....
4800 watts from a belt driven alternator I think is a bit of a stretch or do they drive it differently?
Not a lot of roof space on those generally-you could try some solar ground deployed, even if it's just a few watts it all helps. If you keep moving them to optimum angles they can make power very efficiently. Store them on your bike rack.....

Whinny said:

Edit-I type too slow....

Don't worry about ordering batteries for a bit-today is New Years day-not a lot of work going on.
I don't think you are missing much in your thoughts, it can be that inexpensive for the benefit. You may want to think about the price of the cells-don't necessarily go for the cheapest, look in the forum for group buys.
It's really hard to say how much power you will need, depends heavily on what you are using, A/C is really hard on power. With a soft start device you could probably run it with the Xantrex (if it's pure sine). What other loads does the RV have? I do like that Magnum.....
4800 watts from a belt driven alternator I think is a bit of a stretch or do they drive it differently?
Not a lot of roof space on those generally-you could try some solar ground deployed, even if it's just a few watts it all helps. If you keep moving them to optimum angles they can make power very efficiently. Store them on your bike rack.....

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It's belt driven. And 6000 watts isn't out of line for belt driven alternators. Volta goes up to 8000, ambulances and monster trucks and such use similar systems. It's only something like 14 hp off a 380 hp engine. The 370A XP for sale already puts out 4400w. But think about the cables to move 370A 20 feet.

High draw 120v appliances are the A/C and convection microwave to start, plus I'll have an induction stove. Low draw like the TVs and such should rarely get over 200W.

Toddmccollam said:

There's something called a soft start you can put on the AC which slows down the rotor startup time. We're talking 1/6s to about 1/2s, so not something noticeable to a user. It costs $300 and brings the surge down to...I forget, but you can run the AC on a 2000W inverter at that point. It sounds too good to be true but there are plenty of videos on them, I even found one where an electrical engineer had that exact A/C hooked up to an oscilloscope showing what the soft start can do. And coleman now includes the soft start in some of their A/Cs, so it's a real thing. My point being, the A/C surge shouldn't be a deal breaker.

The 4000W inverter generator the RV comes with is made to run the electric system directly. So yes, with a battery powered RV I wouldn't need that, just something that could charge the batteries. But I like the alternator because it could charge the batteries fast, that 120a 48v one is putting out 6000w. The transit can actually be optioned with a second alternator from the factory (tho it's 12v and only with the ambulance package), so adding it isn't a crazy idea. There's basically a spot designed in for it.

If by multiplus you mean the victron inverter it's too big and not available in the power configuration I want.

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I already forgot you wanted 48v.

One thing to think about is how much battery capacity vs how often you have to run the engine. With a 120 amp alternator you will be able to recharge your 16 280amp hour cells in a little more than 2 hours from dead empty. Your battery bank can run your AC alone (assuming its draws 1500W) for 16 hours not including the microwave, cooktop and other small loads. Based on that, in warm weather, you may have to be driving every 2 days for 2 hours. If your a weekend warrior or always on the move anyway that may be ideal, if you like to park in one spot for an extended stay it could be a PITA.

I have the same capacity as you are planning (at 12v). I do have ac but it is a very small unit and I have very little space to cool. If the future is anything like the past, I go and sit in one spot in the forest for a week or more. For my application I think I can quite easily get 5-7 days out of the battery.

20 foot runs is all the more reason to wait for 48v alt.

Fridge is 12v? I wonder if you would be better with 20 cells-use 4 for the 12v side, converting back and forth has quite a penalty in efficiency. Charge it with a B to B when required and solar....

Whinny said:

20 foot runs is all the more reason to wait for 48v alt.

Fridge is 12v? I wonder if you would be better with 20 cells-use 4 for the 12v side, converting back and forth has quite a penalty in efficiency. Charge it with a B to B when required and solar....

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Hadn't thought of that. More stuff to jam in though, so I'm sure I wouldn't start out there. As far as I can tell, even adding tanks heaters and whatnot in the winter the 12v draw should never get above 1000w.

I do wonder why Volta uses a $2000 48V to 12V converter that can output 3000W in Class B vans. It seems like massive overkill, maybe I'm missing something. But I don't think so, the 12v system is supposed to be low power because it's so bad at moving current.

It seems you have a big summer/winter temperature swing, where is the primary usage going to be?

Whinny said:

It seems you have a big summer/winter temperature swing, where is the primary usage going to be?

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Plan is across the northern US and western US, avoiding the east coast and south.

I find when traveling you don't need to worry too much about topping off batteries fully. Just keep in mind solar options for the future, it does work really well.
I think your travel and power plan is fine.....my opinion might not mean much though!
NW like Alaska or ??

Whinny said:

I find when traveling you don't need to worry too much about topping off batteries fully. Just keep in mind solar options for the future, it does work really well.
I think your travel and power plan is fine.....my opinion might not mean much though!
NW like Alaska or ??

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I've actually been wondering, with that much battery, if I need to put in the alternator to start. I'm not going to full time in the RV, initial trips would be short. If those batteries last a few days in one spot I could overnight at a campground or go home to charge them up and do laundry and order pizza. I think shore power with that charger would charge the battery from zero in around 6 hours. I'll get to the alternator eventually but I don't want to tear the whole RV apart and not use it at first while I spend tons more money and time doing everything at once.

NW like the northern few states, which tend to be fairly forested and empty. Michigan over to Oregon. And the west, New Mexico, Colorado, Utah, etc. Alaska would be nice someday but these will be trips where I need to stop and work during the day, and have internet access to do so. And ski areas across the rockies.

I do want solar but I want to get a roof rack and install the panels to that instead of directly to the RV. But that's a whole other issue, it's not made for a roof rack. The roof's not even flat.