After pricing out decent cells it turned out to be cheaper to get a premade battery from https://www.electriccarpartscompany.com
I went with the BestGo battery pack as seen here https://www.electriccarpartscompany.com/12v-400ah-preferred-lifepo4-lithium-battery-packs
I saw a teardown online of the battery here and it all looked very solid – thick bus bars connecting the cells and BMS.
However, I wanted a battery pack that would talk over CANBUS to the rest of my system, and one that would work with the DVCC option from the Victron solar controller and Multiplus. This would let the BMS control the charge and discharge sources to make sure the battery isn’t overcharged/discharged, as opposed to the ‘old’ method which was setting individual voltage limits on each and every charge/discharge source. In addition, it uses cell voltage values to do this rather than battery voltage and is therefore a lot more accurate.
I settled on the REC BMS as it had a lot of support from Victron and Wakespeed (my alternator regulator). I used this document which may be helpful to others doing the same thing -> link
Firstly I unscrewed the lid of the battery
Then I removed the BMS, being careful not to electrocute myself
Next I rerouted shunt so it didn’t go through the old BMS and instead connected up the new REC
And then connected all the cell taps and I was done!
For now the REC BMS just sits on top velcroed in, but I’d really like to find a way to extend the lid a couple of inches so it will fit inside the battery and cut down on some of the wires everywhere – I have a custom wire loom I got that I could use to drive the contactors!