DIY LiFePO4 build

there still is some cost savings depending on how your order stuff.  for example, due to tariffs and such for you to get the cells int he US right now you are looking at 95 bucks per cell with free shipping I believe, they have gone up an average of 25US a cell in the last few months.  they were cheaper before the tariff crap started happening. 

If you live in Canada and don't mind waiting for the slow boat to deliver them, or know some one in Canada who can order them for you and then you go visit and build your battery.....  I think they can be had for about 65.00 bucks now, would have to check on the price with the supplier. so at 65/cell that is 260 bucks, you can get a 200amp BMS for about 80 bucks CDN so now we are up to say 320US.  you need a fuse, some cables, so say 300 US all in.  I haven't found the elusive 100US 100ah battery most seam to be right around that 200 buck range, but look at 300ah "mini" batteries and see what they are..  I say mini because that's the size that's the same as mine, the other 300AH were made of a bunch of 100AH or 150AH cells in series/parallel so they took up more room.  the new mini's you see are using 304Ah cells so they are the same size as mine.  and the good thing about the mini form factor is you can put two of them in almost every camper out there as they are group 27 size I believe.

so the watt cycle 280Ah mini with Bluetooth is 730.00 the regular price on the renogy 300 mini is on sale for 799, regular 899.  so there still is some savings.  now one thing to note, the cheep batteries have no real compression, they are just shoved in the battery box with some Capton tape or a fixture holding them in place.  so ya as long as your charge and discharge rates are modest it won't make a huge difference, but if your approaching that 0.5C rate in charging or discharging, which isn't hard with a 100Ah battery then compression becomes more important for getting full battery life.

now at the prices I paid for my cells because I got them so long ago, and I got a good deal as we ordered 32 cells.  so I built 4 batteries for other people before I even started on mine but theirs were just to the Kapton tape usable stage, they had to come up with their own case.  I am probably more expensive than buying a new 300AH mini, but I know which cells I am using, but we are comparing prices two years ago to prices now.  two years ago a 300ah premade was over 2000.00 bucks.

another example about 4 months ago a 100ah cell was 35 bucks in the US (from the expensive stores) and 20 bucks on the slow boat from China.  today they are 60 bucks so tariffs have brought back pricing from 2 to 3 years ago.  so you could build a 100ah battery for 120 bucks 4 months ago, now its going to cost you at least 300.  so the larger you build right now the more your going to save as the price of premade is being affected also.  

ya, I am leaning towards not painting it also, then I don't feel bad if I screw something new to the sides haha

there is an engineering aspect to them also, plus the added benefit of them not moving around.  when they charge at higher rates the casing can expand and swell, so by putting between 4000nm and 7000nm (min/max) of compression on the battery pack, it serves to enhance the lifespan and performance of the battery by preventing internal components from delaminating.  It also helps to manage swelling that can occur due to internal pressure during charging and discharging cycles.

so do you need it, its debatable, the cycle life is based on test of cells than are under compression, so by not having them in compression it stands to reason that it will be affected, and eve recommends compression.   For the average rv use though, where our charging is 55amps at max, then on one 100Ah battery it will make a lot of difference in my opinion, but if you have 900ah like my 5th wheel and your only charging at 55amps then you are only charging at 0.06C and that is pretty gentle on the battery.  so the bigger worry would be from vibration of traveling.  there are also people who claims that most of the damage from swelling is done in the first 5 to 10 cycles so you only need compression for that.. 

then there is exactly how much cycle life do you lose uncompressed, some claim that instead of 4000 cycles you might get 2500, that sounds like a lot, but it is still 24ish years with two cycles every weekend, which is why the cheep batteries don't worry about it as it is going to outlast their 5 year warranty unless you abuse it which then the warranty won't cover it anyways..  

for me the benefits far outweigh the extra work, as I do a lot of off roading to get to places so holding the guts of the battery together with compression just makes sense.  I still have to figure out how to do it in the 5th wheel, what I might just do is make the compression fixture the battery hold down under the steps so I just drop the battery into it and tighten the end down.  I have to get under the stairs and see what I have to work with and come up with a game plan for when I put those ones together.