Car Batteries 101

What most people don't know about lead-acid batteries would fill a book, and I'm not going to write one here. I've read the books and have seen about every condition printed in them; but this isn't a chemistry class. It's a short article to let you know what you need to know about common battery problems. With these tidbits you'll know when a battery is worth trying to revive and when it isn't. I'm going to keep the article as simple as possible though some will obviously say, "Yeah, but he left this or that out", and then expound about their knowledge about something they've read in a book or something they saw on an Internet BBS.

That's okay. All I want to accomplish is to better educate some of you guys and gals about how to determine yourself whether or not you have a good battery in that old car you just pulled out of grampa's barn or to allow you to periodically check/maintain the battery you have in that MG you drive once a month on a clear, dry Sunday afternoon.

Testing The Battery

Most places test batteries with a load checker which puts a heavy load on the battery with a big shunt or resistor. This quickly shows the state of charge, but tells nothing about the condition of each individual cell, nor if the battery is likely to hold a charge.

This is where a hydrometer will tell the tale without charging the battery and running another load check. There are several styles of battery hydrometers, but the one that requires the least amount of electrolyte and can be used with even the smallest lead acid batteries is the "pocket" type shown in the photos. They usually cost $6.00 or less and are available at auto parts stores and many discount stores.

The one pictured is a KD brand #2118 bought from an auto parts something over 25 years ago and it works as good today as it did right out of the blister pack. The glass is darkened by residue from being used so many times you can hardly see the four balls, but they show up good in actual use. Check the package and make sure it has clear instructions for use before buying one.

When using a small hydrometer like this always fill the tube twice in each cell and take your reading on the second fill (fill tube - dump back into cell - fill tube again & take reading). The volume of the tube is so small that a high or low reading from one cell can have a bearing on what the next one shows with just one filling. Therefore, we use the first filling as a 'tube flush'.

Refilling Battery Cells

Never add water to a battery before checking with a hydrometer unless it is so low on electrolyte that the tester can't pick it up. In that case, top the cells off with water - preferably distilled water - charge the battery fully, then check it. A hydrometer will find a defective cell even in a battery that appears to be fully charged. When filling a battery use water only, never electrolyte (acid), as this enriches the acid content to a point it will begin dissolving the lead plates or eating away at the plate separators. I never fill a cell higher than about 1/8 inch from the bottom of the indicator ring. This helps to keep acid bearing moisture from gassing out and corroding everything it touches.

Sponsored Links. Become a Supporting Member to hide the ad above & support a small business

Infrequent Use

Batteries that are used the least and not maintained by periodic charging fail much sooner than those in normal service, but even this is not always reason to replace them. When a lead-acid battery sits idle and is allowed to slowly discharge the plates become sulfated. That is, the sulfur in the sulfuric acid migrates to and saturates the lead plates leaving the electrolyte too weak to support interaction between the plates. There are mysterious battery restoring additives on the market and what they do is attempt to desulfate the plates. I say "attempt to", because sometimes they work and sometimes they don't, but a good slow charge at 2 amps or less and checking each cell with a hydrometer will tell the tale.

Two sulfated batteries, restored to working condition

The two batteries pictured here are prime examples of fully sulfated ones being resurrected from the dead. They both sat idle for about two years and tested deader than hammers any way I went at it. Knowing the nature of idle batteries I set my charger at 2 amps, hooked up on one, and let 'er bump for 24 hours. At the end of that time she showed a little promise of coming back from the dead by having each cell float one ball in my hydrometer. I continued to test it every 24 hours for a week and it came to 75% charge on every cell so I took it off the charger and put the other one on and went through the same drill again with the same results. While the second battery was charging the first went down a little, but it went down evenly on each cell, so I put it back on the charger for another 24 hours. The result was a nearly fully charged battery so I hit the other one with another 24 hours and it came up a little more. In the end the Plus Start now has a 75% charge after sitting idle for a month and the Ever Start holds nearly 100% for the same period of time.

Why did I mess with them at all? I was playing. Besides I may put one of them back in service some time, either one should have at least a year of good use left under favorable conditions. I normally get an average of 6 years service from batteries, some more, some less.

Examples

Here is an example of a battery that would be good to go as is. All the balls are floating in both pictures, but the fourth one is not as high in photo 2. The rest of the cells floated all four high but a variance this small is of no consequence even if only half of them floated ball four. Even if some readings had ball four not floating at all it's worth a slow charge to see if they even up. This battery dropped to this stage from 100% charge in about 30 days of no use or charging.

 

I acquired two batteries like this one at once. One was in a 1981 VW Rabbit diesel pickup I bought to rebuild, and the other was in a 1984 VW Jetta turbo diesel I bought for parts and to upgrade the pickup. Both vehicles had new batteries with little or no use and both had sat idle for several weeks before I acquired them. Both batteries were in a low state of charge and wouldn't kick the engines over, however both had low but nearly even hydrometer readings right down the line, and that told me they were probably good ones. I slow charged each one overnight and they both came to 100%. I had no use for them at the time but ended up using one in my Mercedes 300D about a year later and it has performed like new for about a year. After about 2 years I put the other one in the pickup and It too performed like new.

The main point here is that both these marginal batteries were low, but by testing them with a hydrometer before and after charging told they were good to go without any doubts. Installing a used battery with confidence is not possible without knowing the condition of every cell.

This is a battery that served well for seven and a half years in my Scamp camper. It was put to use only a couple of weeks each year but was treated well during it's life. While in use on the road, it was either charged (1) by the towing vehicle, (2) when in an RV parking spot and plugged into 110 volt current the converter in the trailer charged it, and (3) when not in the Scamp it was properly maintained. More than once when squatting somewhere other than in an RV campground it operated the 12 volt lights all evening and two 12 volt fans all night with no perceptible loss of speed by the fans.

It was nearly 8 years old the last time I checked it, and it gave the hydrometer readings you see in the pictures. One cell floated none of the balls and the next floated all of them. There was no need to check any further because two hydrometer readings like these anywhere on any lead-acid battery spells "The End". But, hey, 8 years of RV use?

Hydrometer Test: No balls floating indicates dead battery cell

Hydrometer Test: All balls floating, good cell (same battery...)

While a battery is in service it is constantly being drawn down and charged up again. During this process tiny flakes of material that make up the plates and plate separators are being shed and settling to the bottoms of the cells. Once this residue builds deep enough to touch the bottoms of the lead cell plates it effectively short circuits them and as that cell draws current from the rest in an effort to remain equal it drags them down with it. That's why some evening you may drive a perfectly starting vehicle to the supermarket, do your shopping, and come out to a battery that's "deader than the chicken in your bag" when you didn't leave anything turned on.

Maintenance

Car batteries lined up for monthly charging maintenance

It's important to properly maintain an idle battery, this is how I do it. I place them in a convenient place with the plus post(s) turned toward me so I never hook up one to the charger wrong. About once a month I recharge them at a rate of 2 amperes per hour until they are fully charged. This takes on the order of 15 to 30 minutes each and if the charge meter doesn't drop to zero in an hour I run a hydrometer check on that battery to find out why. Sometimes, like the Scamp battery they just reach the end of their service life all at once, usually because of sediments in the bottom. Some other reasons for sudden death, while in use, are:

• loose or corroded connections, which is easy to repair
• broken cell connector cell plates shaking out and falling down (quite rare)
• the battery is low on water
• a failing or failed alternator
• bad connections or a blown fuse in the charging circuit.

Additional information about battery maintenance and simple equipment to do it can be found in the article "Charge It, Please" in the Library.

I hope this little piece gives you a better insight into understanding lead-acid batteries, and would like to dedicate it to the late Mr. Willis J. Pledger. Mr. Pledger was a very wise but uncomplicated man and my mentor in things mechanical. He was a battery rebuilding guru without peer plying his skills with no fanfare, no fame, but always respected by customers of his handiwork, and all who knew him.

This article was originally published on Tony Barnhill's website "The Autoist" and is reposted by permission.