Lead-Acid Aging: Corrosion, Water Loss & Stratification

Battery Technology Reference · Last reviewed 2026-09-15

Direct answer: Beyond sulfation, a lead-acid battery ages through three mechanisms: grid corrosion (the positive grid slowly oxidises), water loss (overcharge splits water into gas), and acid stratification (the acid concentrates at the bottom in a poorly-charged battery). Heat and overcharge accelerate all three.

The three mechanisms

Mechanism	What happens	Main driver
Grid corrosion	The positive lead grid oxidises and grows, weakening and eventually failing	Overcharge + heat
Water loss	Overcharge electrolyses water into hydrogen and oxygen, drying the electrolyte	Overcharge
Stratification	Denser acid sinks, so the bottom of the cell is over-acidified and the top under-acidified	Partial charging, no gassing

Why overcharge is the common thread

Overcharge drives corrosion and water loss directly: it pushes the positive grid past its normal oxidation and electrolyses water into gas. Stratification is the opposite problem — it happens when a battery is never fully charged, so the acid is never mixed and settles by density. The two failure groups pull in opposite directions, which is why the correct charge profile — neither over nor under — sits in the narrow band between them.

How the technologies resist aging

Lead–calcium grids — reduce water loss and self-discharge (the "maintenance-free" design).
AGM — immobilises the electrolyte so it cannot stratify, and recombines oxygen to reduce water loss.
EFB — carbon on the negative plate improves charge acceptance, reducing the partial-charge state that drives stratification.

The Author's Take

Position: The three aging mechanisms are all charging problems in disguise — corrosion and water loss from overcharge, stratification from undercharge — which is why the charger matters more than the brand.

Reasoning: The battery's chemistry sets its potential; the charge profile decides how much of that potential survives. Understanding the three mechanisms makes the maintenance rule obvious: charge correctly, and the battery ages on schedule instead of early.

This is the author's editorial view, not a purchasing guarantee.

Sources

Battery engineering references — corrosion, water loss and stratification mechanisms.
Manufacturer technical literature — grid alloys and maintenance-free design.

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