As they are not expensive compared to newer technologies, lead-acid batteries are widely used even when surge current is not important and other designs could provide higher energy densities.

The French scientist Nicolas Gautherot observed in 1801 that wires that had been used for electrolysis experiments would themselves provide a small amount of secondary current after the main battery had been disconnected.

Gel electrolyte batteries for any position were first used in the late 1920s, and in the 1930s, portable suitcase radio sets allowed the cell to be mounted vertically or horizontally (but not inverted) due to valve design.

[11] In the 1970s, the valve-regulated lead-acid (VRLA), or sealed, battery was developed, including modern absorbed glass mat (AGM) types, allowing operation in any position.

[12][13] In the discharged state, both the positive and negative plates become lead(II) sulfate (PbSO4), and the electrolyte loses much of its dissolved sulfuric acid and becomes primarily water.

The design of some types of lead-acid battery (e.g., "flooded", but not VRLA (AGM or gel)) allows the electrolyte level to be inspected and topped up with pure water to replace any that has been lost this way.

When used in diesel-electric submarines, the specific gravity was regularly measured and written on a blackboard in the control room to indicate how much longer the boat could remain submerged.

[17][18] Specific values for a given battery depend on the design and manufacturer recommendations, and are usually given at a baseline temperature of 20 °C (68 °F), requiring adjustment for ambient conditions.

B. Thomas and W. E. Haring at Bell Labs in the 1930s and eventually led to the development of lead–calcium grid alloys in 1935 for standby power batteries on the U.S. telephone network.

The advantage of this is an increased surface area in contact with the electrolyte, with higher discharge and charge currents than a flat-plate cell of the same volume and depth-of-charge.

This makes cylindrical-geometry plates especially suitable for high-current applications with weight or space limitations, such as for forklifts or for starting marine diesel engines.

These trade-offs limit the range of applications in which cylindrical batteries are meaningful to situations where there is insufficient space to install higher-capacity (and thus larger) flat-plate units.

To reduce the water loss rate, calcium is alloyed with the plates; however, gas build-up remains a problem when the battery is deeply or rapidly charged or discharged.

AGM batteries often show a characteristic bulging in their shells when built in common rectangular shapes, due to the expansion of the positive plates.

When a normal wet cell is stored in a discharged state, the heavier acid molecules tend to settle to the bottom of the battery, causing the electrolyte to stratify.

The mat significantly prevents this stratification, eliminating the need to periodically shake the batteries, boil them, or run an equalization charge through them to mix the electrolyte.

Stratification also causes the upper layers of the battery to become almost completely water, which can freeze in cold weather; AGMs are significantly less susceptible to damage due to low-temperature use.

AGM cells already have a high acid content in an attempt to lower the water loss rate and increase standby voltage, and this brings about shorter life compared to a lead–antimony flooded battery.

AGM cells that are intentionally or accidentally overcharged will show a higher open-circuit voltage according to the water lost (and acid concentration increased).

Repeated deep discharges will result in capacity loss and ultimately in premature failure, as the electrodes disintegrate due to mechanical stresses that arise from cycling.

If this loose debris rises enough, then it may touch the bottom of the plates and cause failure of a cell, resulting in loss of battery voltage and capacity.

As batteries cycle through numerous discharges and charges, some lead sulfate does not recombine into electrolyte and slowly converts into a stable crystalline form that no longer dissolves on recharging.

Deep-cycle and motive power batteries are subjected to regular controlled overcharging, eventually failing due to corrosion of the positive plate grids rather than sulfation.

Repeated cycles of partial charging and discharging will increase stratification of the electrolyte, reducing the capacity and performance of the battery because the lack of acid on top limits plate activation.

[34] Periodic overcharging creates gaseous reaction products at the plate, causing convection currents which mix the electrolyte and resolve the stratification.

Similarly, in a poorly ventilated area, connecting or disconnecting a closed circuit (such as a load or a charger) to the battery terminals can also cause sparks and an explosion, if any gas was vented from the cells.

Personnel working near batteries at risk of explosion should protect their eyes and exposed skin from burns due to spraying acid and fire by wearing a face shield, overalls, and gloves.

Long-term exposure to even tiny amounts of these compounds can cause brain and kidney damage, hearing impairment, and learning problems in children.

[36] Attempts are being made to develop alternatives (particularly for automotive use) because of concerns about the environmental consequences of improper disposal and of lead smelting operations, among other reasons.

However, the dissolved material is then no longer available to participate in the normal charge-discharge cycle, so a battery temporarily revived with EDTA will have a reduced life expectancy.