When an original BMS flex cable has been used for many charge cycles (over 300, 500, or 1000 times), its charging voltage drops.

For example, on iPhone 11/12 series, the normal charging limit is 4.45V, but after many cycles it may drop to only 4.34V.

Even if you replace the old battery cell with a brand new one, the lower voltage means you cannot get the full capacity. Some of the battery’s potential is wasted.

Here’s how much capacity is lost when reusing an old BMS flex cable:

After 300 cycles: about 5% loss
After 800 cycles: about 8% loss
After 1000 cycles: about 13% loss


That’s why, if you just put a standard new battery cell into an old BMS flex, the user may not feel any improvement in battery life.

StellarXcell Ultra cells are made with 10% more capacity than standard cells.

This extra capacity compensates for the loss caused by the voltage drop. So even with an old BMS flex, the user still feels like they have a fresh, long-lasting battery.