Battery life and total throughput vs DOD

[Circlotron]

A battery manufacturer might say a certain battery will last for 300 full discharges or 1000 partial discharges. In both cases the aggregate energy throughput might be similar. Ignoring time, is there some kind of more or less constant correlation between battery life and total Joules or Watt/hours throughput?

[David Hess]

No, because there are different wearout mechanism at play.

Charging and discharging cause mechanical strain in the structure of the battery which damages the electrodes and separator.  But independent of this in a lithium cell, the voltage across the electrolyte causes damage through electrolysis, so maintaining a high charge state damages the cell by itself.  Supercapacitors have this problem also while lead-acid, NiCd, and NiMH cells do not beyond electrolysis of water which is reversible.

[trobbins]

Circlotron, that characteristic is what is generally seen for VRLA batteries designed for cycling and standby/cycling.  At some level of standby application the performance of the battery degrades from age as there are not enough cycles in its life to reach end of service life from that aspect.

For VRLA that effect may be compromised by cell variations/spread in a monobloc, or monobloc variations in a string, so there also needs to be a maintenance/monitoring effort to avoid those variations from prematurely ending the life of a battery bank in an energy storage system.

[Siwastaja]

Assuming we talk about li-ion, you get a lot more throughput by limiting DOD. Say you get mere 500 cycles at 100% DOD. At 50% DOD, it's not going to be 1000 cycles, it can be well be 5000 cycles or even more. Details vary but this is the general pattern.