Depth of Discharge and Cycle Life: Get the Most From Your Battery

How deep you drain a battery decides how many cycles you get. A small change in depth of discharge can double its working life.

ATB Power · Battery Solutions · 5 min read

Depth of discharge (DoD) is how much capacity you take out before recharging. For lead-acid especially, shallower cycles mean dramatically more cycles. Understanding this is the easiest way to lower your cost per year.

ATB cycle life comparison by series — ATB cycle life by series. Cycle life falls as depth of discharge rises, and lithium delivers many times the cycles of lead-acid at the same depth.

The trade-off

Take a 100 Ah battery. Using 30 Ah is 30% DoD; using 80 Ah is 80% DoD. The deeper you go, the fewer total cycles the battery delivers before it reaches end of life (commonly 80% of rated capacity).

Depth of discharge	Lead-acid (typical)	LiFePO4 (typical)
30%	Most cycles	Very high
50%	Good balance	High
80%	Fewest cycles	Still 2000+ cycles

Lithium tolerates deep discharge far better, which is one reason it lasts so much longer in daily-cycle duty.

Practical guidance

For lead-acid cycling, size the bank so average use stays near 50% DoD or shallower.
Recharge promptly; sitting discharged is as damaging as deep discharge.
Avoid routinely going below 20% state of charge on lead-acid.
Heat shortens life too: every sustained 10 C above 25 C roughly halves it.

Sizing tip

If your daily load is 50 Ah and you want 50% DoD on lead-acid, specify about 100 Ah of usable capacity. With lithium you can size much closer to the actual load.

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