On Wednesday, October 16, 2019 at 7:51:15 PM UTC-5, kinsell wrote:

Unfortunately, not all LFP batteries have a BMS, and of those that do,
not all have low-voltage cutoff. Of all the misinformation that gets
spead about on LFP's, that right at the top of the list.

Given how easy it is to add a low-side power switch, I wonder why you
would build an automated, computer controlled tester that lacks this.
Adding it would make it useful for a wide range of batteries.

Kinsell - You have me thinking now.

While both my Stark and Bioenno batteries has a BMS that cuts off at 10Vdc, it wouldn't be too difficult to add an Arduino relay shield to the mix. It could remove the load for non-BMS lithium batteries and for SLA's.

These shields contain four 3A 24Vac relays and cost about $4.50 (cheap! see https://www.ebay.com/itm/323801575423). The neat thing about these shields is that they stack and make a nice tidy package. I would have a stack of;

LCD Display
-----------
Relay Shield
-----------
Arduino

Once the battery charge drops to the low volt trigger point, I would remove the load (turn off the relay) from the battery via coding. One relay rated at 3A should be ok but I might use two relays in parallel to be sure.

I just ordered a couple of the relay shields and will report back.