Fortunately, batteries are easy to take care of, once you understand some basics.   In this article, we will explain the basics of battery operation, show you how to check the condition of your battery, and how to perform routine maintenance.

Minimum Battery Maintenance:

At a minimum, have a look at your every two months.  Look for:
  

• Look for signs of leakage or seepage from the caps.  If you see seepage, wipe it clean with a paper towel & throw it away immediately in a plastic bag and rinse you hands in water.  Better yet, get a spray can of battery terminal cleaner to use with the paper towel.  This stuff has acid neutralizer in it and makes the whole job safer & easier.

• Next look for corrosion on the terminals.  If you find any, clean the outside of the terminals with a wire brush and inspect further for corrosion between the posts and clamps (if there was any corrosion at all, it's probably there too). If you need to disconnect the terminals, read your service manual for information on removing power from your car; Some cars like BMW's and others, require special procedures to avoid removing power from the electrical bus if possible.
  Clean the posts & clamps with a battery post cleaning tool or wire brush, and use the spray cleaner too.

• Check the fluid (electrolyte) level in each cell & add distilled or reverse osmosis water if needed. 

 
OPTIONAL (But recommended)

• Place a charger on the battery.  If the charger reaches 5 amps or more, watch the charger for a few minutes.  With a good charging system & battery, 5 minutes or less above 5 amps is about right.  If the battery continues to charge at a 5 amp or higher rate for more than 5 minutes, let the battery continue charging until the battery is fully charged.  At this point it's time to think about why your vehicle's charging system is not keeping the battery fully charged.  Have you been in slow traffic with the lights on?  I have found that on my car, driving when it's 115 F outside, slow traffic, A/C on max, it can take 1/2 hour or more to charge the battery after stopping.

If your driving conditions are demanding on your battery, like extreme heat or cold with slow traffic, it may be wise to manually charge your battery once in a while.  Keeping the battery at or near full charge all the time will extend it's life.
 

Advanced battery maintenance begins with all the steps in basic maintenance and goes from there. 

Important Concepts

A car battery is really a chemical storage device. It converts chemical energy into electrical energy and back.   It does this using positive and negative plates, submerged in an electrolyte (Sulfuric acid & water).

As the battery is discharged, the sulfuric acid in the electrolyte is converted to water, the lead peroxide negative plate is converted to lead and lead sulfate.  The positive plate is also converted to lead sulfate.

During charging, just the reverse happens, and the electrolyte acid content is restored.  It is important to understand what happens to the electrolyte during charge and discharge, because determining the condition of the electrolyte is the main focus of advanced battery maintenance.

As it happens, sulfuric acid is very heavy and weighs a lot more than water.  So when you mix sulfuric with water, the resulting electrolyte is heavier than water.  Because the acid in the electrolyte is changed to water as the battery is discharged, we can determine the charge state of a battery by measuring the specific gravity (it's weight compared to water) of the electrolyte.  This measurement is greatly affected by temperature, so it is important to know the temperature of the battery when doing measurements.  We use a hydrometer to measure the specific gravity of the electrolyte (see photo).

Battery electrolyte is usually about 35% sulfuric acid by weight.  This means that a fully charged battery has an electrolyte specific gravity (SG) of about 1.265 at 80 degrees F.   As the battery is discharged, the SG declines to about 1.240 at 2/3 charge, and finally to about 1.150 in a fully discharged battery.

By the way, a "12 volt" battery is not really 12.0 volts;  Each cell of a fully charged battery produces 2.10 volts in each cell (there are 6) for a total of 12.6 volts.

Again, temperature counts a lot:  As the battery gets colder, the electrolyte gets denser, making the battery look more charged than it really is.   As the battery gets warmer, the electrolyte get less dense, making the battery look less charged.  The correction factor is 0.004 for every 10 deg. F away from the standard, 80 degrees F. (see Temperature Correction Table below)

S.G. Temperature Correction Factor for Lead/Acid Batteries

What's Normal

Well, now that we know all this neat stuff, how do we put it to use?  To begin with, we can use a hydrometer together with the chart above to find out how much charge a battery has.

It is important to measure the S.G. in all 6 cells.  A normal battery should have approximately the same S.G. in each cell.  If it does not, there is probably a problem with the battery.

As mentioned above, a normal battery that is fully charged produces 12.6 volts, not just 12.0 V.  (Remember, when measuring battery voltage, everything in the car should be off, or the battery should be disconnected.  Voltage measurements are always "no load" measurements unless the battery is being tested for it's performance under load).

Common Battery Problems

While batteries are very reliable for the most part, there are some common problems that can develop:

Batteries that sit unused for long period of time can be damaged if they are allowed to sit in a discharged, or partially discharged condition.  When a battery is discharged, the plates are converted to lead sulfate. Charging converts them back to lead & lead peroxide. When a discharged battery sits for a long period, the lead sulfate tends to harden and resist converting back.  A battery in this condition is referred to as a sulfated battery.  If a battery in this condition will still take a charge (a badly sulfated battery will not) then it may be saved by charging it until there is no increase in S.G. for about 2 hours, and then charging it at a slow rate for 48 to 60 hours.  If this does not restore the battery to a full charge (as measured by S.G.) the battery is toast. This is a common problem on boats, farm equipment, and spare vehicle that are not often used.  Lesson: keep those batteries charged when they are being stored.

Another common problem is the "dead cell".  Sometimes, a battery will have just one cell go bad or short out.  When this happens, the battery will seem fully charged, but fail to start the car, or it may start the car right after charging, but then fail to start the car an hour or more later.  If this happens measure the S.G. in each cell.  If one cell has a lower S.G. than the rest by a significant amount, replace the battery - there is no way to fix this problem.  This condition most often happens to batteries subjected to lots of vibration, and sometimes to new and almost new batteries that have a bad cell from the factory.

Drive safe!

-Gordon

Comment or questions? email me at: gordon@partsavers.com