I use a Batrium BMS and can see the cell voltage sag pretty easily when charged full and discharge occurs. You won't see it as much of course once below 3.4V until you get to the lower knee. Same with charging, 304's tend to run more than the 280's from the data I have.
Don't get me wrong, these cells are perfectly fine for use in a solar system. It's just the little things that you see from different cells. I still recommend the 304's over the 280K given the price point and test results I have. I just don't care for someone saying the 280K were somehow sold dishonestly when the lowest cells I tested all came within 1% of the stated capacity. I received what was advertised. Does the same person measure the beer in each bottle before they drink it to see if it is outside a 1% window of the stated volume?
Over time, the 280K might actually have longer cell life, better balance and less voltage sag compared to the 304's. Or the 304's might indicate the cells are far superior to the 280N or 280K.
