Eco worthy 20a MPPT vs TS-MPPT-60 and series test

When you have a dieing battery the voltage rises fast and drops just as fast when you put a load test on it. The 8-D is a starting battery that I bought used a few years and has been abused repeatedly with my inverter, microwave and air conditioner test. As a core it is worth half of what I gave for it, so it isn't a big loss. I'll be nicer to it's replacement.