We do not list nickel-cadium batteries in this catalog because of their high cost and environmental problems related to disposal. We do specify nickel-iron batteries in some situations. They have proven to be very reliable, but most PV modules do not have a high enough peak power voltage to charge them adequately. The size of the battery bank required will depend on the storage capacity required, the maximum discharge rate, the maximum charge rate, and the minimum temperature at which the batteries will be used. When designing a power system, all of these factors are looked at and the one requiring the largest capacity will dictate battery size.
Temperature has a significant effect on lead-acid batteries.
If one amp is used for 100 hours, then 100 amp-hours have been used. A battery in a PV power system should have sufficient amp hour capacity to supply needed power during the longest expected period of cloudy weather. There are many different sizes and designs of lead-acid batteries, but the most important designation is whether they are deep cycle batteries or shallow cycle batteries. Shallow cycle batteries, like the type used as starting batteries in automobiles, are designed to supply a large amount of current for a short time and stand mild overcharge without losing electrolyte. Unfortunately, they cannot tolerate being deeply discharged.