I've been intrigued by Lithium leisure batteries for a while now, not something new but not something I really knew much about. This post is just about replacing a lead Acid / AGM leisure battery with a Lithium one and the steps involved. 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 leisure battery on roadtrips, after a few days the 'fade' of lead acid (like a torch getting dimmer) was giving me problems mainly around getting my heater started, 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. Its the discharge curve that attracted me to lithium. Lithium-ion and Life Phosphate (LifePo4) give everything for 80% of the time. After appx 40% and lead acid battery isn't giving the volts I needed. So I decided in order to find out more to build a Leisure battery from scratch and 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. I was getting replies and posts but I understand now the people posting probably weren't so familiar with whats what and just jumped in. 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, maybe one after the other (called in series) 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. 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 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. 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 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 batterys charge using a different rating, its called a C rating and it blew my mind a bit to be honest. The battery I got 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 cycles (charges), they are sold with marketing 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. 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 guess about 1/4 of the weight for the same capacity lead acid battery. So what do you need to build one. How much?. March 2023 cost. Cells 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. 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 Battery Capacitor 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 but I don't need solar so can't go into that. 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 too 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. 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. So how to.... Assuming you bought all the above Batteries arrive like this Each cells is 3.2 so they need to be connected to give 12v. This is the video I used. (Click to open YouTube connect BMS video) This guy also does the BMS setup video later. I followed what he did Number the cells and connect in series. 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 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 in my mind is still +ve and negative post What you will do is have a lead (65A red cable) from #4 +ve and your -ve 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 theres a limit to number of images I can upload each post. Use the chassis as your earth to connect P-
cont.. I made a box with some carpet underlay inside to protect it. The great thing about lithium is no fluid, its solid state so I laid mine on its side in the rear opposite side of the starter battery in a crude box. 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. View attachment 130390 The DC to DC charger I placed underneath the armrest, it was a perfect fit. View attachment 130391 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. 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 https://youtu.be/1EpHGK-Un0U you can shut the whole system down and tweak it 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 which threw me for half an hour but I eventually realised what I had done. I've since added a temp controlled relay to my coolbox (@Lasty nice to meet you fella) and sorted out my volt drop so all is good, can't wait to try it out. PG
I would take it all apart and top balance them first. You may find one cell always reaches a higher voltage sooner Sent from my Pixel 6 Pro using Tapatalk
