How fast and deep cycle is determined on lead-acid battery?

[Willen]

I have two batteries- both has almost same sized plates inside (has transparent body of battery so inner thing is visible).

One is known as 'deep cycle' for solar energy and has little large area to hold more than 2 liters acid.

Another known as 'fast cycle' for motor bike and has narrow space to hold less then half liter acid.

Is this an only one difference between fast and deep cycle battery's composition? Or other...

 

[NorthGuy]

Deep cycle batteries usually have much thicker plates causing slower operation.

Start batteries have very thin plates. Thin plates have much bigger surface area to produce very high current when needed.

 

[KeepItSimpleStupid]

The major difference is the plate separation. The "fast cycle" battery also can deliver more short-circuit amps (e.g. CCA or Cold Cranking Amps) than a deep cycle battery. There is probably a plate thickness issue too.

Depleting the charge cause crystals to form and they more easily short the plates when they are close together. The charing process is not exact, so some may remain on the plates after charging.

There should be info at www.batteryuniversity.com

 

[Mosaic]

The major difference is the plate separation.
Depleting the charge cause crystals to form and they more easily short the plates when they are close together. The charing process is not exact, so some may remain on the plates after charging.

I'd like to comment on this if I may:

Plate thickness, quantity and composition is the major difference. Deep cycle batteries tend to use more pure lead in the plates vs lead composites made of a powder slurry in a lead grid. This makes the plates more robust and less permeable to the electrolyte. This increases the internal resistance per plate square area and thus makes deep cycle unsuitable for high amperage pulses as required by starter battery systems.

Depleting the charge causes amorphous lead sulphate to form on the plates (reversible process), this can become crystalline if the battery remains undercharged. This crystalline form is resistant to decomposition back into sulphur and lead (during charge) thus causing a reduction in serviceable plate area over time and battery 'weakening'. The sulphur that forms the lead sulphate is drawn from the sulfuric acid electrolyte, reducing the concentration of the electrolyte which also adds to the battery's internal resistance due to increased conductivity losses. Battery equalization can reverse this in mild cases.

Crystals which 'form' to short the plates are NOT sulphate crystals as these do NOT conduct. This is related to the composition alloy of the lead plate (can contain calcium, silver and antimony) and is essentially dendrites of 'plated' lead forming on the lead plates which cause cumulative 'soft' shorts which increases the battery's self discharge to the point of being useless.

In order for this lead electroplating to occur, the battery must be in a discharged state for some time, which causes the lead sulphate to slightly dissolve in the weak electrolyte. Then upon recharging this lead can be 'plated' onto the plates...After a few such cycles the dendrites (whiskers) can cause the shorting between plates. This process happens more efficiently in warmer conditions. It is reversible with advanced pulse charging and reflex charging systems.

Ancel