Winterizing Your Flooded Lead Acid Solar Batteries
By Real Goods Solar Tech Noah Mervine
Winterization is an important part of wet (flooded) cell battery maintenance. If your renewable energy system’s battery bank uses wet (flooded) lead acid batteries, be sure to follow your battery manufacturer’s maintenance guidelines (or our guidelines below).
Note: Our Battery Life Savers Desulphators minimize maintenance and are a great addition to any lead acid battery bank. When permanently connected to your lead acid batteries, a BLS Desulphator keeps the batteries healthy and even extends their lives by breaking up the lead sulfate that builds up on the plates over time as you charge and discharge them.
Deep-Cycle Battery Winterization Checklist
- Check the electrolyte – The electrolyte level must always be ABOVE the plates, but should JUST TOUCH the plastic that extends down into the cell. Do not fill all the way to the top!
- Check for corrosion – Small amounts of corrosion on the terminals should be scraped off. If you find excessive corrosion, turn off the power, disconnect the battery cables, then scrape and scrub with a wire brush. In either case, apply a corrosion guard coating where necessary. All copper and steel on the battery should be completely coated to prevent further corrosion.
- Ensure tight connections – Apply some force to the cables to see if they’re loose. Follow manufacturer’s recommendations (or ours: “Tight, but not gorilla tight”).
- Measure cell voltages – With batteries at rest (or with voltage stable), check the voltage of each cell in the bank. Larger differences indicate a greater need to equalize.
- Fully charge & equalize at 73°F. If your charger does not have a battery temperature sensor module (BTS), voltages should be adjusted appropriately for temperature. For a 12-volt battery bank, the absorb voltage should be 14.9V and the equalization voltage should be 15.4V. For voltages other than 12V, multiply or divide as appropriate (see table below).
Nominal Battery Voltage Absorb Voltage Equalize Voltage 2V 2.48 2.56 6V 7.45 7.7 12V 14.9 15.4 24V 29.8 30.8 48V 59.6 61.6
- Leave charge controller/solar circuit ON – If you’re going to be away for weeks or months, adjust the Absorb voltage down to around 14.1 to 14.3
Battery Maintenance Tools
As you perform this yearly maintenance on your solar batteries, you may find you need some special battery tools or replacement cables. We’ve linked some helpful battery maintenance products we carry on RealGoods.com below.