Figure 3 illustrates a normal battery in which the acid is equally distributed form top to bottom. This battery provides good performance because the correct acid concentration surrounds the plates. Figure 4 shows a stratified battery in which the acid concentration is light on top and heavy on the bottom. A light acid limits plate activation, promotes corrosion and reduces performance. High acid concentration on the bottom, on the other hand, artificially raises the open circuit voltage. The battery appears fully charged but provides a low CCA. High acid concentration also promotes sulfation and decreases the already low conductivity further. If unchecked, such a condition will eventually lead to a user-induced battery failure.

	Figure 3: Normal battery The acid is equally distributed from the top to the bottom in the cell and provides maximum CCA and capacity.
	Figure 4: Stratified battery The acid concentration is light on top and heavy on the bottom. High acid concentration artificially raises the open circuit voltage. The battery appears fully charged but has a low CCA. Excessive acid concentration induces sulfation on the lower half of the plates.

Allowing the battery to rest for a few days, applying a shaking motion or tipping the unit over tends to correct the problem. A topping charge by which the 12-volt battery is brought up to 16 volts for one to two hours also reverses the acid stratification. The topping charge also reduces sulfation caused by high acid concentration. Careful attention is needed to keep the battery from heating up and losing excessive electrolyte through hydrogen gassing. Always charge the battery in a well-ventilated room. Accumulation of hydrogen gas can lead to an explosion. Unlike many other gases, hydrogen is odorless and can only be detected with measuring devices.

Acid stratification is difficult to measure, even with the EIS technology. Non-invasive testers simply take a snapshot, average the measurements and spit out the results. Stratified batteries tend to show higher state-of-charge readings because of elevated voltage. On preliminary tests, the Spectro CA-12 also shows slightly higher CCA and capacity readings than normal. After letting the battery rest, the capacity tends to normalize. This may be due to diffusion effects in the stratified battery as a result of resting. Little information is available on how long a stratified battery needs to rest to improve the condition. It is known, however, that higher temperatures will hasten the diffusion process.

Ideally, a battery tester should indicate the level of acid stratification; sulfation, surface charge and other such condition and display how to correct the problem. This feature is not yet possible. Much research is being done in offering more complete battery evaluation without the need to apply a full discharge. This knowledge can then be applied to other battery systems, such as traction, military, marine, aviation and stationary batteries