SOH is a measurement

SOH (State of Health) expresses a cell's real capacity relative to its original capacity. A cell rated 3,000 mAh when new, returning 2,550 over a full cycle, shows an SOH of 85%.

The key word is returns. SOH is not estimated by eye or from the battery's age: it is measured, by charging and discharging the cell at controlled current on a bench and counting the energy actually delivered. Two cells from the same pack, the same age, can read 91% and 68%.

What each grade covers

We grade cells on that measured SOH, cell by cell:

  • Grade A — SOH ≥ 90%: closest to new, low internal resistance. For premium packs and demanding applications where current matters.
  • Grade B — SOH 80 to 90%: the best capacity-to-price ratio. The reference grade for stationary storage and solar self-consumption.
  • Grade C — SOH 70 to 80%: more modest capacity but perfectly usable at low duty: backup, top-up storage, undemanding circuits.

Below 70%, we do not resell. The remaining capacity no longer justifies the disassembly and reassembly work, and the pack would age too fast. Those cells go to material recycling, as explained in recycling or reuse.

SOH does not tell the whole story: internal resistance

This is the criterion listings almost always omit. A cell can show good SOH and still perform poorly if its internal resistance has risen.

That resistance drives voltage sag under load and heating. A cell at 90% SOH with degraded resistance will run hotter, return less usable energy at high current and age faster than its capacity suggests.

So we measure both, and every product sheet gives resistance in milliohms next to capacity. A grade A at 22 mΩ and a grade B at 38 mΩ do not serve the same uses.

Why homogeneity beats grade

Here is the most counter-intuitive point: a pack of matched grade B cells beats a pack mixing A and C.

In a parallel group, the weakest cell sets the pace. It discharges sooner, recharges earlier, takes a relatively heavier load — and therefore degrades faster, dragging the group with it. A pack is never better than its weakest cell.

Hence our rule: cells are sorted by grade and matched by measured capacity within a batch. Buying a consistent grade matters more than buying the highest one.

Choosing the right grade for your use

The useful question is not “which grade is best?” but “what does my application need?”

For home solar storage you discharge slowly over hours: grade B is ample, and paying for grade A adds almost nothing. For high-current use — repeated starts, power peaks — grade A and its low internal resistance earn their place. For rarely used backup power, grade C is the rational economic choice.

Every batch ships with its measurement data. You know what you are building in, and our Pro Shop shows capacity, SOH and resistance for each reference.