New flooded lead-acid batteries begin to deteriorate from the moment they are shipped from the manufacturer. Just sitting on the dealer's shelves for a long time can reduce their capacity.
The self-discharge rate of these batteries can be on the order of 10-15% per month @ 70 degrees F. Some have reported even higher rates, depending on the antimony content.
When batteries are left in less than a fully-charged state, they begin to sulfate. Lead sulfate crystals (PbSO4) form on the plates, and can grow and embed themselves into the surface of the plates, thereby permanently reducing capacity. This is the principal reason for early battery deterioration and failure.
New battery capacity -- in the store -- can vary considerably, even as much as 30-35%.
Contamination, corrosion of the positive plates, stratification of the electrolyte, and other factors contribute to the deterioration of the battery's capacity.
Given these considerations, what should you do with new batteries?
- Exercise them....give them a deep discharge -- down to 40 or 50% of their rated capacity (or about 12.1 volts measured with all loads removed and sitting for at least 8 hours), then give them a really full charge, using a smart charger properly sized for the battery bank.
- If possible, do this a few times, though once will help a lot.
- Some authorities recommend an equalization cycle for new batteries (i.e., a controlled "overcharge" @ 15.5V or a bit higher for 8 hours or so). This helps considerably to knock any PBSO4 crystals off the plates.
- Add only distilled water -- never acid -- until the plates are covered about 1/4" to 3/8".
- The use of HydroCaps or WaterMiser caps to reduce water loss is a good idea, as it greatly reduces the loss of water and extends the time period between adding distilled water.
- Check the battery fluid levels frequently (very easy to do with these caps fitted).
- Keep the batteries fully charged...float level of at least 13.2-13.5 volts....and exercise them periodically.
- The use of a pulse-type charger (like the Iota series with the IQ-4 smart-charge option) will help to maintain your batteries in a healthy state for a long time.