Jumping back a bit, I had crummy luck with the $100.00 batteries from big box stores.
For the Lithium batteries, you need one BMS for the full pack voltage. You can group cells in parallel, and then series, to get the AH and voltage you want to run.
The biggest safety risks arise from over charge, over current and over discharge. Which is why you want a BMS. One of the jobs of the BMS is to watch that the cells are all close to the same charge level. Under charge, overcharge, out of balance, over current all trigger the SSR to open. There are also limits on temperature extremes for charging and discharging, which should be look into before deciding which type of battery you choose. My tractor is stored and charged in a temperature controlled environment, so a lot of these problems I don't have. I did also install fans on thermostats to cool them if needed, If I were to run in the sun in summer, etc.
The batteries I got were surplus ones made for BMW i3 cars. I have a bunch of pictures on facebook, or I can send some via email. Dave On 11/27/2021 4:01 PM, Rob Brockway via Elec-trak wrote:
Some thoughts on batteries. Sam’s club has Duracell gc2 for $89 plus core charge. A little higher at Batteries plus bulbs. I have been watching lithium batteries on Ebay and Amazon. The two things I keep watching other than price: 1. Do they have the battery management set up to allow for 200-300 amps for short periods. The cheaper units have low maximum amps. I don’t think 100 amps would work for anyone with hilly terrain. 2. Safety. I worry about the safety of lithium and the potential for fire. Does anyone have any thoughts about these factors? Rob Sent from my iPad