Over on the Off Grid Ham affiliate Google Groups.io forum a reader asked a question about how to properly maintain flooded batteries, also referred to as wet cell batteries. We have addressed this topic before but as a result of recent interest it’s a good time for a flooded batteries refresher course.
Safety gear for flooded batteries is not expensive or hard to find. You probably already own most of this stuff. Here’s what you’ll need:
- Safety glasses.
- Acid-resistant rubber gloves. Leather works good too.
- Long sleeve shirt, long pants, and shoes that you don’t mind being ruined.
- A box of common household baking soda.
- Water –tap water is fine.
You’re going to get sulfuric acid on you. It’s almost unavoidable. You may not notice right away when acid gets on your clothes. After a while, holes will appear. Leather seems to hold up well.
You also may not immediately notice if the acid gets on your skin. An itchy/burning sensation will come on slowly. Rinse any exposed skin with water. If there are any visible injuries or the itch/burn does not stop, seek medical help.
Neutralize spilled acid with the baking soda.
Flooded batteries give off very explosive hydrogen gas. Make sure you are working in a well ventilated area. It should not need saying but I’ll say it anyway: No smoking, sparks, or open flames!
The bottom line.
Working safely with flooded batteries does not require a lot of knowledge or training. The key concepts are: Do not allow any contact with the sulfuric acid, vent away the hydrogen gas, and eliminate electric shock hazards. If you do those three things you’ll be fine.
Tools & equipment.
The tools & equipment needed for maintaining flooded batteries is mostly simple stuff. More advanced amateurs will want additional items but here are the basics:
- Adjustable wrench, pliers, open ended wrenches, or Vise-grips.
- Wire brush.
- Spray-on anti corrosive compound (auto parts store).
- Hydrometer (auto parts store).
- Distilled water.
- Funnel or measuring cup.
- Optional: Load tester.
Auto parts stores have brushes made specifically for flooded batteries.
Spray on anticorrosive compound avoids corrosion on terminals. Some old timers use a water & baking soda mixture to clean battery terminals. This method removes the crud that’s already there but will not prevent corrosion going forward.
Use only distilled water in flooded batteries. Never use tap water, home filtered tap water, nursery water, or other bottled waters. Everything except distilled water has minerals and trace additives that will contaminate your battery.
The hydrometer is such a handy tool that it gets special mention. Battery and off grid retailers sell hydrometers for $30.00 and even more. You don’t need to spend that much. Hydrometers are available on line or at any auto parts store for less than twenty bucks. Make sure you get one for testing batteries because there are also hydrometers for automotive coolant and other liquids and they all basically look the same.
A hydrometer is the only practical way to check individual cells within the battery. The principle is very simple: As a flooded battery charges and discharges, the density of the acid changes. By measuring this density, you can very accurately determine the state of charge.
If everything is right, all the cells should have about the same density. If the densities are all over the place, your battery may need to be equalized.
Equalizing is the process of bringing each cell to the same state of charge. This is also referred to as balancing. Some of the better battery chargers and solar controllers have an equalize setting. The process can take several hours. When the equalization cycle is complete, check the fluid densities again. If they all closely line up, then you are good to go. Your battery may need to be replaced if the hydrometer still shows one or more cells are undercharged. At the very least, it has diminished capacity.
Here is a handy chart to interpret density readings.
Taking care of business.
Regular maintenance on flooded batteries should be done at least twice a year, or quarterly if your batteries are cycled often.
The procedure is simple. Start with a fully charged battery. After taking appropriate safety precautions, check the voltage of the batteries with a multimeter. Record the reading. Carefully check the exterior of the battery for cracks, bulges, fluid leaks, and any abnormal conditions. Use the wire brush to clean the terminals. Wire brushing may not be needed if you used anticorrosive compound when initially installing the batteries.
Pop open the filler ports on your batteries. Look inside and verify the fluid levels. Then check each cell’s state of charge with the hydrometer. If the fluid levels are really low, you may not be able to draw enough up to get a reading. That’s not good! If you encounter this situation, fill the cell per instructions below. Do not check the density with the hydrometer until the battery has gone through a charge cycle. You will not get a meaningful reading immediately after filling a cell with a large volume of water.
Low fluid levels can be caused by one or more of several things:
- Excessive heat
- Cracked or damaged case
- Filler caps not properly installed
- Battery not sitting on a level surface
- Infrequent/improper maintenance
Fill ‘er up.
Use a funnel or a cup with a spout to top off each cell with distilled water to just below the filler port. Completely immerse the plates in fluid. Do not tap, hit, or rock the battery in an effort to release excess gas bubbles. “Burping” a battery serves no useful purpose. It can crack the case or cause internal damage. Wipe up any spilled fluid and reseal the battery.
After the battery charges, check the voltage again. It should be equal to or greater than than the voltage recorded at the beginning of the procedure.
What we learned today.
- Flooded batteries need ongoing maintenance for maximum capacity and service life
- Sulphuric acid and hydrogen gas can be very dangerous and requires some simple but important safety precautions.
- A hydrometer is the only practical way to determine the state of charge in specific cells of flooded batteries.
- Equalizing or balancing is the process of bringing each cell to the same state of charge.
- Service your flooded batteries every six months, or every quarter if they are in a harsh environment or cycled often.
This Off Grid Ham article from August 2016 gives additional information about flooded batteries.
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