LiFePO4 Battery Know How

There is a lot of information on the net and I cannot and do not want to be exhaustive. However, this page is intended as a basic explanation of the project – the battery part. Part 1: What you need to know. Part 2: The building of the batteries. And always remember: “With great power comes great responsibility!”

Part 1: What you need to know about LiFePO4

  • This link contains much in depth and practical information:
  • There are three types in general:
    • Round cells (like 18650) that have a wrapped internal structure.
    • Prismatic cells that have a block shape, as a wrap or layered like a curtain, hence prismatic ( /\/\/\ ).
    • Pouches are layered without any support structure – you have to create that yourself.

Bloating of batteries

  • Batteries may bulge a little and even some new batteries are not completely flat, even though they perform well.
    • In principle, swelling is not intended.
    • However, expansion and contraction are part of charging and discharging LiFePO4 cells.
      • There is also gas formation, which is why there is a valve, usually between the electrodes.
      • Just search for “LiFePO4 swelling” to get an impression. This is a document explaining it a bit more.
      • My personal opinion: Lock up pouches, don’t lock up prismatic cells. Always choose a construction that can absorb expansion and shrinkage to a limited extent.
        • It does not seem a good idea to me to clamp cells between two thick wooden plates with threaded rods.
        • An alternative could be to make a sleeve of thin material in which they fit. But: opinions differ on this, despite my mechanical engineering background.


Prismatic cells are tested before they leave the factory. Grade A is top. If they are stored for a few months they become grade B – not a bad battery. Quality decreases alphabetically to sometimes Grade F – you don’t want these.

Before buying, you want to make sure that you do not buy garbage – probably the hardest part.

SOC – State of Charge

  • The most important thing is to treat the batteries properly. This way you will have the longest enjoyment of the battery.
    • Do not overcharge and undercharge, keep the voltages within limits and…
    • Limit the charge and discharge current.
    • Don’t store and use in hot spaces.
    • Don’t charge at temperatures below 0 Celsius.


  • Bad contacts are not only showstoppers, they can also cause a fire while giving the impression that everything is in order, i.e. working.
  • Because this is not mentioned in so many articles and videos, I mention it here with exclamation marks!!
  • Always prepare contacts.
    • Dry the contact surfaces.
    • Sand the surfaces with 300-grit (or a bit more) paper.
    • Then clean with isopropanol.
    • In wet or condensing spaces: Apply a good moisture barrier such as petroleum jelly.
  • As with contact surfaces, tightening torques are rarely discussed and, look at the videos, people even do hand-tightening. Unbelievable and please, take it very seriously!
    • At least use proper online tables for this.
    • Do not over-tighten or under-tighten connecting screws. If you regard a threaded rod as a spring, you can make the spring a little longer by adding one or two washers before tightening the screws. For M6, a battery tightening torque of 7 Nm is mentioned, but check the manuals.
  • Crimping terminals? Always double check the quality if it is not your daily activity. Use the right tools and match wire sizes with terminals. Personally I post solder crimped connections often.
  • Read this:

Part 2: The building of the batteries

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