How To Care for Your Batteries
Batteries vary by chemistry and configuration, which means that the required maintenance also changes. Some of these maintenance tasks may be automated or performed remotely via charge controllers or battery management systems, including charge regulation, voltage checks, and related measurements. Others require on-site manual operations or oversight. These tasks include, but are not limited to, adding water or equalization.
Sealed lead-acid batteries, gel cells, and absorbed glass mat (AGM) batteries are often called maintenance-free, because they don’t require manual maintenance like watering or an equalization charge. While this makes them suitable for remote or unattended power systems, sealed batteries need accurate regulation to keep them from overcharging or over-discharging.
Lead-acid batteries should be recharged as soon as possible, with no exceptions. This is because the positive plates change from lead oxide to lead sulfate as it discharges. Should the plates be allowed to stay in a lead sulfate state instead of immediately charged, the plates will remain partially sulfate even when fully charged.
Parts of the plates that are sulfate cannot hold energy any longer, which reduces the effectiveness of the batteries and their lifetime. For example, batteries that are only partially charged on a regular basis tend to fail in less than a year. While new lead-carbon batteries dramatically reduce sulfation, they still need to be recharged immediately to keep them in good working shape.
Remember, battery warranties never cover damage due to poor maintenance or loss of capacity due to sulfation, so proper maintenance is key.
Wet-cell or Flooded Batteries
Wet-cell or flooded batteries need their electrolyte levels checked at least once every three months. At the same time, the batteries will need to be topped-off with distilled water.
However, water should not be added to fully discharged batteries. As these batteries discharge, they absorb electrolytes. If water is added while the battery is discharged, then the battery is recharged, the electrolytes will overflow and create a safety hazard.
The tops of the batteries should be kept clean and cables should be tight. If the cables are loose, do not attempt to tighten or remove them while charging or immediately after charging. Any spark around the batteries has the potential to cause a hydrogen explosion inside the case, igniting a fire or causing a larger explosion.
Should the batteries show a variation of 0.05 or more in specific gravity from one another, they will need an equalization charge. This is essentially a steady overcharge that brings the batteries to a bubbling state.
With proper care as outlined above your batteries should remain in good working condition throughout their service life and serve well as part of any power system.
How To Measure Battery State-of-Charge
Essentially, battery state-of-charge (SOC) can be easily measured using an amp-hour meter, by voltage, or by specific gravity. Measuring SOC by voltage or specific gravity requires specialized knowledge and a great deal of care, so it is recommended that owners utilize amp-hour meters for all battery systems.
An amp-hour meter is somewhat like a fuel gauge for batteries, providing all the information necessary to keep the batteries charged. While using an amp-hour meter, users can see the system’s voltage, current, and battery condition.
The voltage of a particular state-of-charge will vary depending on which state the battery is in; charging or discharging. Also affecting the variation is the current in relation to the size of the battery. It is important to remember that voltage will vary with temperature.
While the battery is charging, a lower outdoor temperature will increase battery voltage. For example. the full-charge voltage on a 12 VDC battery is 0.9 VDC higher at the lower temperature of 32℉ than at 70℉. The opposite is true for discharging. While discharging, a higher outdoor temperature results in higher voltage.
While a battery is idle, the temperature has little effect, although very high temperatures may increase the self-discharge rate.
A hydrometer may also be used to measure battery state-of-charge in flooded lead-acid batteries by measuring the amount of electrolytes near the plates. However, the electrolytes can only be measured at the very top of the battery, which may or may not be near the plates.
To get an accurate reading from the hydrometer, take the readings after the battery has been idle for a long while, or after several hours of the battery slowly discharging. Near the end of the charging cycle, gas bubbles rise through the sulfuric acid. It takes a few hours to mix enough to get an accurate reading with the hydrometer.
Whether a hydrometer or an amp-hour meter is used to measure battery state-of-charge, using them will allow you to determine where your batteries are in the stages of charging or discharging.