Cheap batteries mean not as good quality control and not as tight tolerances. So your internal resistance can vary a lot from cell to cell.
We only buy LiPos from Thunderpower and we request that they come from the same batch and ir are matched as close as possible. We’ve never had issues with batteries but then again we do not run them hundreds of cycles. My personal RC LiPos also from TP are perfect after 1.5years of use, I only balance once every few charge cycles and make sure I don’t discharge beneath 3.2V.
As far as cycles on Liions. From the 25R spec sheet: “Cycle life: With standard charge and maximum continuous discharge. Capacity after 250cycles, Capacity ≥ 1,500mAh (60% of the nominal capacity at 25°C)” Sure, we do not run them at max continuous discharge but I do not see this number being any higher than 70% after 300 cycles at our discharge rates. All the info is in the datasheets, I suggest looking it up, you’ll learn more that way than asking others as there is a ton of useful information on them.
E: Cellphone batteries are lipos