Choosing Between a Single Large Lithium Battery or Two Smaller Ones (1 Viewer)

Oct 14, 2007
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As in the title, whats the thinking on Lithium batteries, is it better to have one large one or 2 smaller ones? My thinking is if you only have one and it goes boobies up your stuffed and if you have 2 the duff one can be isolated from the bank. Or are they that reliable that one would be ok?
 

bigtwin

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Depending on the manufacturer you may find that you get a higher discharge current limit (important if using an inverter) from two batteries than from a single larger battery. This is a function of the BMS in each battery.

Two gives redundancy, one is simpler from a monitoring perspective.

Whichever way you go, I’d definitely make sure that the BMS has bluetooth functionality. Whether you feel you need integral battery heating for low temperature charging is up to you.

Ian
 
Apr 27, 2016
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The size of lead-acid batteries was always limited by the weight, and the difficulty of heaving a large battery into a confined space. A lithium battery can get more storage into the same weight, but it's still a big consideration for installation in vehicles. A 110Ah lead-acid is about 23kg, and and a 216Ah LiFePO4 is about 28kg.
 
Oct 12, 2009
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I wonder whether the redundancy for one Lithium could be covered by carrying a small(75Ah?) lead/acid not connected to the system but available.

I presume all chargers can be switched to lead/acid, which would suffice until Lithium is replaced if it goes Phut. Lead/acid could be kept charged occasionally.

Any thoughts?

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Lenny HB

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I wonder whether the redundancy for one Lithium could be covered by carrying a small(75Ah?) lead/acid not connected to the system but available.

I presume all chargers can be switched to lead/acid, which would suffice until Lithium is replaced if it goes Phut. Lead/acid could be kept charged occasionally.

Any thoughts?
Or just to keep going buy a cheap LA if you have a failure.
 
Aug 26, 2022
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I recently bought a new 230 lithium to fit under a Ducato front seat, this was to replace a single AGM. On arrival the new lithium was reading 10.4v and the Bluetooth etc was not working. It had to go back to the supplier, which took over 2 weeks to collect, due to Christmas, with goodness knows how long I would have to wait to get it inspected, repaired or exchanged and returned to me.
This got me thinking that Lithium being a specialist battery and not available over the counter will present real problems if it goes belly up while on a trip. And with the current waiting time of months for most popular sizes, then getting an exchange is not going to be straight forward. Imagine trying to get one back to the UK from Spain and then an repair or exchange sent out to wherever you happen to be stranded. So : it was a refund for me and 2 x AGM are now in the van. At lest of one of them goes down I have redundancy and I can pretty much get another one over the counter anywhere in Europe.
 

bigtwin

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At lest of one of them goes down I have redundancy

How would you know if one of them had gone down? By the time you’d figured out that one was kn*ckered they’d probably both be kn*ckered.

At least with LiFePo4 batteries you get a BMS that will alert you of any problem with an individual battery.

Redundancy versus single point failure is a different issue from SLA versus LiFePo4.

Ian

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Jan 30, 2020
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How would you know if one of them had gone down? By the time you’d figured out that one was kn*ckered they’d probably both be kn*ckered.

At least with LiFePo4 batteries you get a BMS that will alert you of any problem with an individual battery.

Redundancy versus single point failure is a different issue from SLA versus LiFePo4.

Ian

Very good point… Bluetooth BMS’s on my two Lithiums gives good insight into performance and health 👍🏻
 
Aug 26, 2022
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How would you know if one of them had gone down? By the time you’d figured out that one was kn*ckered they’d probably both be kn*ckered.

At least with LiFePo4 batteries you get a BMS that will alert you of any problem with an individual battery.

Redundancy versus single point failure is a different issue from SLA versus LiFePo4.

Ian
Good point about knowing if one goes down. A reduced discharging time and the voltage dropped down faster than normal would be my only way. When my pair of AGM have had their day I will be revisiting lithium and having seen the complete failure of the single lithium battery, I am still minded to fit 2 x smaller ones...
 

bigtwin

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When my pair of AGM have had their day I will be revisiting lithium and having seen the complete failure of the single lithium battery, I am still minded to fit 2 x smaller ones...

Two smaller lithiums may well give you a higher current discharge limit than a single larger battery too; something to bear in mind. 👍

Ian
 

MisterB

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enough to know i shouldnt touch things i know nothing about ....
As I previously suggested, getting what fits best got me thinking about the potential of identifying an unused irregular shape space and making a battery to fit that space (as a one off obviously), there are loads of you tube videos demonstrating how to build your own battery out of cells, but they all seem to be very much of the same shape as off the shelf batteries.
Perhaps building your own battery to fit an irregular shaped space which would be otherwise 'under utilsed' could be an option?
 

bigtwin

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Perhaps building your own battery to fit an irregular shaped space which would be otherwise 'under utilsed' could be an option?

It could. 👍

Particularly if you were enthusiastic about the challenge.

Ian
 

Peppadog

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I recently bought a new 230 lithium to fit under a Ducato front seat, this was to replace a single AGM. On arrival the new lithium was reading 10.4v and the Bluetooth etc was not working. It had to go back to the supplier, which took over 2 weeks to collect, due to Christmas, with goodness knows how long I would have to wait to get it inspected, repaired or exchanged and returned to me.
This got me thinking that Lithium being a specialist battery and not available over the counter will present real problems if it goes belly up while on a trip. And with the current waiting time of months for most popular sizes, then getting an exchange is not going to be straight forward. Imagine trying to get one back to the UK from Spain and then an repair or exchange sent out to wherever you happen to be stranded. So : it was a refund for me and 2 x AGM are now in the van. At lest of one of them goes down I have redundancy and I can pretty much get another one over the counter anywhere in Europe.
Lack of wide availability is a good point at the moment. The market is still minority and specialist.
I've bought my Victron B2B charger and expected to own a 200ah or so LiFePo4 for under my Ducato seat by now. But no one seems to have stock until the end of March. KS Energy indicates a delivery time in 1-3 days, but my email and 2 days of calls to him/them to check availability gets only a recorded message saying he's currently not available. So clearly not there.
Its looking like a second agm at the moment!!
 

bigtwin

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Lack of wide availability is a good point at the moment. The market is still minority and specialist.
I've bought my Victron B2B charger and expected to own a 200ah or so LiFePo4 for under my Ducato seat by now. But no one seems to have stock until the end of March. KS Energy indicates a delivery time in 1-3 days, but my email and 2 days of calls to him/them to check availability gets only a recorded message saying he's currently not available. So clearly not there.
Its looking like a second agm at the moment!!

Mark at Life Batteries has stock. 👍

Ian
 

Peppadog

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Thanks Ian. It doesn’t look like he has one that fits, but I'll have a chat with him.
 

Peppadog

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Thanks. Yes I spoke to Chris at Roamer a couple of days ago. He knows his stuff I think, but did not have a suitable battery in stock.

Still no contact from KS Energy!

I’ve also now spoken to Mark at Life Batteries. He offered me a very good deal on 3 x 50 ah batteries which, amazingly, look like they will fit the space. Two should arrive on Tuesday. If they fit as we think, the third will be a day or two later.
 

Tude

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I’ve gone for roamer 460amp less complicated having one battery cells balance up better less wires. When I asked roamer and other manufacturers they all said one is better than two 🤷‍♂️

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Apr 24, 2018
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I replaced 2 x 100ah LA with 2 x 100ah lithium. Total mass reduction from 50kg to 27.4kg. The 1 x 200Ah option was the same mass. With 2, as has been intimated by OP, in the unlikely event of failure of one battery, I can disconnect it. However, I report I have been heavily using the set up every day for 3 months in winter, they have been very reliable so far.

Because the 100ah are smaller, packaging is easier, there are more options where to put each of them. I put both batteries under a bench allowing me to put the MPPT/B2B under the seat where one LA used to be and easily connect to the Electriblock via ideal diode.

I configured the two small Lithium batteries in an ‘L’ shape, allowing me to fit into the same ‘services’ space my safe, other electrical installations, my compressor and storage tank. I wouldn’t ave been able to do that with one large 200ah.

Bluetooth BMS allows viewing of charge and discharge status of both individual batteries, as well as individual cell voltages. No issues with worries over knowing if one has gone down or is even developing a fault.

As others have said, it’s good to be aware of peak discharge capacity, one big may often be better than 2 small, but not always. My 2 x 100ah each have a max discharge of 100A, giving me a peak discharge of 200A, which is the same as the 200ah option. 200A of discharge is easily enough for a 2kW invertor.

All things equal, due to the advantages in my case as stated, for me, 2 small was a little better than one big. It is likely that one big from the same maker will be slightly cheaper than 2 small, it’s a fine balance.

If going with 2, it is critical to ensure, for the sake of most effective load balancing that the batteries are connected properly, this means the discharge leads must connect to the positive and negative posts of different batteries, with the batteries connected in parallel with the largest possible cables, and with minimum distance between the batteries. It is much more important with lithium to have small distance due to the typical use of invertors, where high discharge loads can create a
voltage drop issue. I use a 180A RNL fuse between batteries and invertor. The additional wiring complexity will likely be a reason why the vendors and installers will normally recommend one battery, and they are correct to do so in most cases.

For me, the £50 premium (for 2 small) was worth it as I obtained advantages from having two - I wanted the redundancy, and I wanted options on packaging. It was the best solution for me.

Finally, whether you go with one or multiple, Lithiums are fantastic, they are hugely better than Lead Acid. It’s a great upgrade for a moho.
 
Last edited:
OP
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Diabalo
Oct 14, 2007
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dawsey Thanks for your very comprehensive input , all comments are helpfull to anyone contemplating changes to their setup. I am leaing more towards 1 large battery now, my worry was if it went down but as Lenny HB pointed out in an earlier thread if it does just buy a LA battery until the Lithium can be sorted out.
 
Apr 24, 2018
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dawsey Thanks for your very comprehensive input , all comments are helpfull to anyone contemplating changes to their setup. I am leaing more towards 1 large battery now, my worry was if it went down but as Lenny HB pointed out in an earlier thread if it does just buy a LA battery until the Lithium can be sorted out.
Thanks. Though I don’t understand the idea of ‘just buy a LA’ if it goes down,

In the event of your single Lithium battery failing while on tour :

1. if it is in warranty, and even if the manufacturer immediately accepts the claim you are looking at at the very least a week before a new battery arrives. If you have to first return the battery, and/or you are overseas it could be much, much longer…

2. If out of warranty, you are looking at at maybe a day or two before you go buy a replacement Lithium from a dealer (they are becoming pretty widely available) and obviously a big bill..

I guess the suggestion of ‘go buy a lead acid’ applies mostly to the first situation, where you are waiting for a warranty replacement. Remember, you would still be forking out a non-recoverable £150ish, you will have to find a battery that ‘fits’, and more minor points, once it’s fitted, you may need to adjust charge profiles and your usage etc. Remember, the risk of both situations can be partly or fully mitigated by having two Lithium batteries…
 
Oct 23, 2022
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As in the title, whats the thinking on Lithium batteries, is it better to have one large one or 2 smaller ones? My thinking is if you only have one and it goes boobies up your stuffed and if you have 2 the duff one can be isolated from the bank. Or are they that reliable that one would be ok?
I currently have a 155Amp Lithium Battery and it has done everything I need., just make sure your regulator is an MTTP for your solar panel
 

stuartforrest

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Aug 14, 2022
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Thanks. Yes I spoke to Chris at Roamer a couple of days ago. He knows his stuff I think, but did not have a suitable battery in stock.

Still no contact from KS Energy!

I’ve also now spoken to Mark at Life Batteries. He offered me a very good deal on 3 x 50 ah batteries which, amazingly, look like they will fit the space. Two should arrive on Tuesday. If they fit as we think, the third will be a day or two later.
I also spoke to Roamer and KS Energy. Roamer guy told me I needed to place pretty much all of the electronics in my motorhome to use a lithium battery which sent me off speaking to motorhome installers who were utterly confused with what I was wanting doing so I had mostly given up but then I spoke to KS energy and they said their battery would work just fine with the equipment I had and I installed it and so far it has been absolutely amazing. I basically swapped out my old battery for the LS Energy battery and now we are drowning in power and I can run a 3kw inverter Very happy.

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