Routine maintenance can prolong the life of a flooded deep-cycle battery bank

By Jeff Myles, marketing manager of Rolls Battery

After the cold temperatures of winter, it’s time to check back on those batteries. Year-round battery maintenance and care is important with any residential battery-based PV system. However, seasonal off-grid and grid-tied installations require added consideration and preparation when left idle in freezing temperatures.

Getting batteries ready for post-winter surge
Whether operating a residential battery-based PV system year-round or seasonally, it is important to maintain sufficient charge on the batteries. Deep cycle lead acid batteries, flooded or sealed, will freeze and damage in cold temperatures in combination with discharge.

Many battery-based solar installations are designed with the intention of limited season or periodic use. Cottages, seasonal rentals and lodges are often left unattended or inaccessible during winter months. In these situations, a decision must be made whether to keep the system active, maintaining a float charge on the batteries, or powered off, leaving the battery bank fully charged and disconnected for storage while not in use.

Seasonal systems in which battery banks are held on a float charge in colder climates should be monitored regularly. PV panels should be kept clear of snow, ice and other debris. A PV system unable to generate power due to snow-covered panels will continue to draw power, discharging the battery bank.  If the property is inaccessible for extended periods of time and weather conditions are a factor, relying on the system to maintain a float charge is generally not recommended.  In these situations, battery banks often freeze due to gradual discharge and low specific gravity, resulting in permanent cell damage, case cracking and electrolyte spills.  In some situations, the damage may not be visible and is identified once the batteries are placed on charge.

Disconnected deep-cycle lead-acid batteries will naturally self-discharge when not in use. The rate of self-discharge increases as ambient temperature rises. As a precaution, stored batteries should be recharged, at minimum, every 90 days until they are back in service to avoid over-discharge, sulfation and possible freezing when temperatures drop considerably.

An inspection should be completed to verify the batteries are still in good working order before placing on charge. With flooded batteries, specific gravity and voltage readings should be taken and electrolyte levels checked in each cell, adding distilled water as necessary. If the battery bank has frozen or show signs of damage due to freezing, do not attempt to charge.  Allow all cells to thaw completely, inspect for damage, perform a voltage test and replace any damaged cells prior to charging.

Seasonal maintenance

As part of a seasonal maintenance routine, Rolls recommends cycling and completing a preventative equalization at the beginning and end of the idle period to prevent prolonged sulfation build-up and possible capacity loss.

Conditioning seasonal battery-based PV systems prior to use is important. Three to four weeks before resuming use of the system, begin to lightly cycle the batteries over a one-week period, ending with a corrective equalization of the battery bank. Where multiple strings of batteries are used, run the corrective equalization on each string individually and reconnect to the system prior to cycling. This will begin to remove any build-up of sulfation that has accumulated while resting on a float or partial state of charge for extended periods.

From summer to winter, daylight hours for PV power generation often vary. Charge times may also require adjustment from the previous season.

It is important to inspect, disconnect, clean and properly re-torque each connection on a regular basis as part of a battery maintenance routine. Loose terminal connections increase the chance of spark or arching, which is a potential fire hazard. When reconnecting, each terminal connection should be greased to reduce damage and corrosion and prolong the life of the battery bank. Proper maintenance will preserve battery performance and life.