DIY Lifepo 12 Volt Battery

6 June 2020

My Nissan Leaf is a 2011. The 12 V battery does not have a date on it so may be 9 years old. Other Leaf owners have reported problems with there 12 V battery so I'm worried mine could die soon.

There is a chance it has already been replaced - (I should do a capacity test on it to check!)

I've also got some "5 Amphour" LeFePo4 cells from a few old e-bikes that would be perfect for building a replacement 12 V battery. So that's what this project is about.


  • I've measured up the existing Leaf battery and designed a new box that I will 3D print.
  • I'll pick the best recycled 40 cells I've got to create a 40P4S LiFePO4 pack with a nominal voltage of 12.8 volts and a capacity of somewhere around 40 Amphours - which is what the original Lerad Acid battery had.
  • I've bought a BMS rated at 80 Amps
  • And a battery monitor meter
  • I've already printed the top of the battery box

One of the advantages of this battery over the installed Lead Acid one is it'll be a lot lighter.


  • weigh the old and new batteries to compare
  • capacity test the existing battery to see how's doing
  • print the battery box base (it'll take 2.5 days to print!)
  • capacity test all my LiFePO4 cells, and select the 40 best ones
  • solder the cells together
  • attach two sets of balance wires (the second set is for cell level testing prior to sealing the battery)
  • add the BMS
  • add the battery level monitor
  • add the main output wires
  • test it
  • pack the cells in with closed cell foam to dampen vibration
  • screw down the led
  • install in the car (can I do this in a way that avoids powering down all the 12 V devices in the car?)
  • more testing
  • if all goes well - completely seal the box lid with silicon sealant.

Cheers, Paul

Page last modified on 07 June 2020 at 01:14 AM