How to - Lithium Leisure Battery Build

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I've been intrigued by Lithium leisure batteries for a while now, not something new but not something I really knew much about.

its over a couple of posts as there is a limit to how much text can go in one post.

This is just about replacing a lead Acid / AGM leisure battery with a Lithium one and the steps involved in building one for yourself, save a ton of money too. Its not a recommendation or anything, just what I've done and sharing the experiences I've had.

Why did I want to do this, build a lithium battery ? I was having problems with my old lead acid leisure battery on roadtrips, after a few days the 'fade' of lead acid (like a torch getting dimmer) was giving me problems, getting my heater started was driving me mad, my heater needs a load of energy to start up then happily runs with a lower draw. Anything less than a tip top LB wasn't cutting it, it wasn't much fun up in the Pennines knowing you're sitting in a van with a great heater but due to fade the bloody thing wouldn't start up.
Its the discharge curve that attracted me to lithium. They don't fade, just full whack for (touted as 80% but realistically I'd say 65%) of their power then they go to sleep.

Discharge-curve.jpg

Lithium-ion and Life Phosphate (LifePo4) give everything for 'up to' 80% of the time vs lead acid battery is dying pretty much over 40% and fades. Simply wasn't giving me the volts I needed to get the heater on.

So I decided to find out more to build a Leisure battery from scratch. This post lays it out if anyone else wanted to have a go. I can also hold my own now and want to get rid of some false information which bamboozled me at the start.

Got to say a big thanks to Geoff (77 Westy) for giving me answers and explaining a lot of this as I was fumbling around in the dark.

So Lithium batteries, a fact of life now and will probably replace lead acid/agm batteries as leisure ones but they can be hellishly expensive. Building one.. its like riding a bike, difficult until you've actually done it, then you could do it without too much thought.

So a couple of rumours to dispel.
"You can't mix lead acid and lithium batteries in your van"
Well no, not as far as physically joining them together you can't but as far as 2 different types in your bus, lead acid starter and a lithium leisure battery, absolutely fine, no problem at all. Because you never actually connect the batteries together, you go through something called a DC to DC charger.

So as that's the first thing I have mentioned I'll explain a DC to DC charger. Also known as a battery to battery charger. A loose cousin of a split charge but its very different. What you are doing is connecting the batteries together via a special DC to DC charger, also called a battery to battery charger.

It is NOT split charge. You can reuse the wiring but the lithium battery does not connect to the alternator and there's no relay.
What happens is you connect both batteries (which run DC current not like AC in your house hence DC to DC) into the DC to DC charger.
IMG_20230317_101552.jpg This is mine in the side pod under the armrest.

Your alternator (white wire above) provides a trigger to tell the charger to start working when engine running. Similar to split charge once your starter battery is full then the Leisure Battery (LB), via the DC to DC charger, draws its charge from the starter battery (all controlled carefully by the DC to DC charger) and the DC charger keeps your batteries happy. Your starter and LB never actually physically connect.

Charging. Who remembers Gunson chargers !. I had one and had to undo the top of my batteries to stop them exploding. The old method was to leave your charger on overnight/ 12+ hrs connected to your battery. They put out 2 amps, maybe 5 if its a special one. Modern chargers you can just leave, trickle ones.

Lithium batteries charge using a different rating, its called a C rating and it blew my mind a bit to be honest.

The battery which I'll go though in a bit has a C rating of 1 (one). It is really important to know what your C rating is as you don't want to over cook it. What does that C rating mean?. Lithium has really low internal resistance, almost none, so if you have a 100ah battery with a C rating of one it means you can charge at 100amps and in 1 hour the 100ah battery will be fully charged. Your old 2 amp or 5 amp charger is not much good.
So in 1 hour you could charge your leisure battery full from empty if you had a 100amp charger.

But the reality is you won't as they are expensive, I bought a 36 amp one so in theory I could charge my lithium LB to full in about 2.5 hours.

The DC to DC charger also happens to be 40 amps so if I drive for an hour I put 40 amps back into my LB.

I haven't run long enough to know if this is true but on paper that's what it does.

Lithium batteries can also take more charging cycles, they are marketed in terms of number of cycles in the 1000's whereas AGM or lead acid is in the low hundreds so again in theory my lithium battery will last 10 times longer at least. So Halfords new battery, good for say 300 charges, lithium in the 5000 ball park !

But as I said the thing I really liked about lithium was the discharge graph.
Lead acid when it goes a bit weak fades. You can't take a lead acid battery much below 50% before it starts to damage it but a Lithium battery delivers full whack for 80% of the time then falls off a cliff. But you have a things called a battery management system that protects it so you won't damage it.

Weight, lithium batteries are light, I'd guess about 1/4 of the weight for the same capacity lead acid battery and at least half the size.

 

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So what do you need to build one. How much?.
March 2023 cost .

Cells. You are buying LifePO4
I got mine from AliExpress but it took 4 attempts, there's a lot of dubious sellers out there. Most never shipped or showed a shipped receipt/tracking to 'London' somewhere etc but I didn't lose any money.
The vendor who came good is a gold supplier and I found they were prompt to answer questions . Tracking was rubbish but the battery cells turned up. I used Global Power LT store.
You buy cells, each is rated 3.2v so you need 4 as 4 x 3.2 is your 12v battery.
I got 105 ah cells . 4 of these was c£153.12 incl shipping.

BMS
You need a Battery management system, a BMS. I bought a 80A BT, LiFePO4 4S 12V BMS from hibms official store (also on AliExpress) which cost me £35.64
Note about these, it says 80A but that's its theoretical discharge amps. Input is half that, 40 amps. The BMS is the brains and you can connect your phone to this.

Indoor Charger
You would benefit from a indoors charger. I bought a 12V 36A from the Good Battery and Green Environment Store, also Ali, for £49.36. Since then I can strongly recommend you buy a variable charger so when you balance you can set Volts at 3.2 and later when assembled you can charge at 14.7.

Battery Capacity Meter
A battery health meter/reader is nice to have, and cheap, was £5.12 from
ThinkingLeader Store
Battery Capacity Indicator DC 8V-100V Lead Acid Lithium LiFePO4 Car Motorcycle Voltmeter Voltage Gauge 12V 24V 48V 72V

Cabling and terminals
Load of cabling, I bought 7 meters of black and 7 of red 65amp cable and 12x 65amp terminals cost me £50 from local car store

Quick Release Plugs
Anderson plugs, these cost me about £10 for a packet of 10
*note about the terminals, a good crimper will handle these solid metal ones, I did it on the 'yellow' crimp slot and it crimped these no problem. I then squeezed them up a bit more and shrink wrap sleeved them.

I also put in another fuse box in the rear just for ease, £8
and some wood and corner brackets (to build a battery box) say £5

DC to DC charger £112
I got a Renogy 40A one. If you sign up to Honey you can get discount codes etc.
You could live without this and just get a home charger but then it won't charge when you are out. Me and the Mrs do off grid road trips so charging while driving is important.

So that's £430 in total.

Some number crunching and you can see the battery cells on their own, battery, nothing else, only work out to be about 36% of the total cost. Its the other stuff around it you need that pushes the price up, and this isn't solar which needs other controllers etc.

If you just want weekend power you could just buy battery, BMS and a charger. Charge it up before you go then when you get home charge it back up.

I did find my old wiring had a problem, back in the day in order to to share the load (amps) i'd doubled up 16a cable which had worked, but plugging in my lithium battery the volt drop was huge. I don't know why it showed up now but I do know the cause was due to small gauge wiring so I used 65a to my heater and now volt drop is only 1 volt max. That's irrelevant to this post but I thought I'd share it anyway. All fused of course.

Amps use:. Imagine you have a fridge, you need to know how much amps it uses, you need to know how much everything uses. It might tell you use in Watts, or it might be helpful and tell you the actual amps but this is important.

So your battery, lets say you have 65 amps of usable power from your lithium battery. Turn that into money, you have 65p in your pocket to spend on energy. You are off grid so don't have any more.
My fridge uses 33Watts at 12v. Not especially helpful but here is what you do. Divide 33 by 12. so 33/12 = 2.75. That's amps p/h so my fridge uses 2.75p per hour of my money.
10 hours 27.5p, 20 hours thats 55p... I've only got 65p in my pocket !.
Lights use about 1p, radio maybe 5p so you can see you have to be careful. I fitted a temp controlled relay (£7) to turn my fridge off when it hit temperature (its a £25 coolbox) so now with the relay when it hit temp would shut down, 50% saving. Also ice packs and taking frozen food we could easily manage a long weekend.

Back to battery, next thing is getting it all connected. And when you buy your BMS make sure its got bluetooth, you set it up from your phone. Again not difficult when you know how but it threw me a bit first.

 

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So how to....
Assuming you bought all the above batteries arrive like this
IMG_20230311_121719.jpg

They need to be balanced, they will eventually balance themselves but you can speed up the process. You connect the cells in parallel so all +ve connected, all -ve connected (NOT series) and connect your variable charger that you have set to 3.5v output to the +ve and -ve and then charge at 3.5v for a day to get them all equal and balanced.

You can charge as high as 3.65 but you will shorten their life, I typically setup about 3.5 to be honest. 3.65 is a bit rash.
In parallel you essentially have one big 3.5v battery.

Once balanced disconnect then reconnect in SERIES, now you will have one 14v battery (4 x 3.5v)
This is the video I followed.
(Click to open YouTube connect BMS video)
This guy also does the BMS setup video later. I followed what he did

Now number the cells and connect in series.
IMG_20230311_172721.jpg


connect batteries.jpg

You connect the cells in series. Bit of paper in between because someone on youtube advised it I couldn't see why not. You number the cells back to front and connect the cells and BMS.

It ends up like this

IMG_20230312_150925.jpg
I used some tubing i had laying around to keep the BMS (on the left) away from the battery to help with heat dissipation. Nobody said to do this but I just did.

Now you have made a 12v battery. #4 above will be your +ve and from the BMS that black wire is your negative. This was how it looks on paper. B+ (from #4 +ve on your cells is +ve and P- is -ve

You can see here, I connected the charger to what is +ve and -ve
IMG_20230312_111638.jpg
What you will do in vehicle is have a lead (a 65A red cable) from #4 which is the +ve and your -ve (also 65amp) is the BMS P- cable.

I have these 2 cables, with ring terminal on the end, poking outside my box to which I connect a 3 tail leads, one to the DC to DC charger, one to the fuse box in the rear and one to my amplifier.
Pictures of box in next post as there's a limit to number of images I can upload each post.

Use the vehicle body as your earth to connect P-

lithium layout.jpg


I made a box with some carpet underlay inside to protect it. The great thing about lithium is no fluid, its solid state so you can lay it on its side. Mine are in the rear opposite side of the starter battery in a crude box.

IMG_20230313_142629.jpg

** Whatever you do when you run the lead from your main battery to the DC charger (you run one from Lithium and one from starter) label up the main battery leads (or DC if you want) so you know what what when they come out the other side.

 

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The DC to DC charger I placed underneath the armrest, it was a perfect fit.

I drilled cable holes through my spare wheel well and into the engine bay. I connect all leads using Anderson connectors and bought an earth terminal block from screwfix to attach earth connections.

IMG_20230326_190936.jpg

That looks really messy but its working ok for now.

Once its in you need to configure your BMS. Same bloke as above (and thanks @77 Westy for finding this)
Click this

you can shut the whole system down and tweak it
Screenshot_2023-03-12-11-23-16-316_com.inuker.bluetooth.daliy.jpg


If your DC to DC charger is working correctly it'll give you a green light when ign is on. I totally forgot to connect the -ve to my main batt -ve (thats the DC2DC NOT the Lithium LB) which threw me for half an hour but I eventually realised what I had done.
IMG_20230317_082446.jpg

IMG_20230317_101602~2.jpg Green is good

I've since added a temp controlled relay to my coolbox and sorted out my volt drop so all is good.

Since I did this I decided to go a bit further and have since put in a 300ah LB. Bit of a bugger I have not had a chance to use it properly as I broke down last year and engine is coming out to figure whats what.

PG

 

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let me know if images aren't all there, it went a bit haywire when I uploaded such a long post

 

[NickP]

So impressive. I'm gonna check this all out when I have time, as been wanting to do similar.