2.7 ohms is close to C1 discharge (15Ah 24V battery), no?
Funnily enough I have a box here with the bits needed to build a proper constant current discharger, with a counter of seconds on it It’s just that the incentive to build it surfaces just once a year…
C1 rate should discharge in 1h to 20V if full rated capacity (by definition) .
Cap checks at C1 rate always last <1h except a brand-new, top-5-percentile battery.
Ideally you should have a constant 15A discharge, but a constant resistor is good enough for your purpose, I just think you need more like 1.5ohm