FWIW, I got my sketchy super cheap lithium titanate battery in the mail, and did some testing. It was advertised as 40Ah but these cells are either defective or used since I only got around 32Ah out of them. Weight is 15.6lbs, but in reality the BMS is kind of unnecessary and this package could easily be under 15lbs. So it's comparable in nominal capacity to the stock group 51R lead acid on the MR2 Spyder. Pics here:
Lithium Titanate Battery - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
Now the cool part: I drained it nearly all the way and plugged it into a Porsche 981 2.7L. It cranked quite slowly at 10.7V, but the engine started. It actually started again in that state after I reset the BMS (some shutoff got triggered when I turned the ignition off), but the starter was spinning the engine for quite some time, so I decided to let it charge. Then it charged at around 100 amps for a few minutes, and at 11.2V, I started the engine 6 times in a row, immediately shutting it off, and it was cranking strong.