Rich’s Repair Ramblings #5: Electrical 101, The Battery


 This article is the first in what will be a continuing series about our old car’s electrical systems. I’ve worked with automotive 12 volt (12V) electrics both as a professional and as a hobbyist for many years, and I’ve enjoyed it. I’ve also been bemused by my fellow technicians, many of whom put me to shame with their mechanical know-how, who plead ignorance or fear of their car’s electrics. It is my hope that these articles will encourage you to tackle some simple fault-tracing and repair on your own jalopies, and feel comfortable doing it.

Let’s start with the battery, the ‘heart’ of your vehicle’s electrical system. If your collectible is a U.S.-made car that pre-dates the 1950s, it most likely has a 6 volt (6V) electrical system. Domestic cars switched from 6V to 12V systems in the mid-1950s, and also almost universally changed to a negative ground system. Some foreign cars stayed with 6V and/or positive ground systems through the 1960s. For simplicity’s sake, I’m going to stay with 12V negative ground systems here, but much of what is covered is applicable to any vehicular electrical system.

Flooded-cell battery. Note electrolyte caps and hold-down clamp.


There are two types of batteries commonly found in today’s cars: the ‘flooded cell’ (wet) battery, and the AGM (absorbed glass mat) battery. The flooded cell battery is the older technology, and it requires checking the water level (really the electrolyte level) and topping it up as necessary. Water is ‘consumed’ as the electrolyte is released as gas through vents during the charging process. If an owner allows the electrolyte level to drop too low, the battery might not hold a charge and could be ruined.

Modern wet batteries have evolved into ‘low maintenance’ or ‘no maintenance’ versions, which theoretically don’t need top-ups. Older flooded cell batteries have removable caps to add water; low- or no-maintenance batteries have caps which require a little more effort to access, if they have caps at all.

The AGM battery holds its electrolyte in glass mats, which minimizes consumption and makes it truly maintenance-free. AGM batteries are completely sealed (no caps) and leakproof, and therefore can be mounted in almost any position. They also tend to be longer-lasting, albeit a bit more expensive than wet batteries.

AGM battery in my Alfa is mounted sideways in trunk.

Whether flooded or AGM, a 12V battery consists of 6 cells; in a fully charged battery, each cell is 2.2V, so 2.2 x 6 = 13.2V. In reality, a static car battery will usually measure around 12.5V. The battery has a positive (marked +) post and negative (marked -) post protruding from the top of the case (GM used side-case-mounted battery terminals for years). A heavy battery cable, typically red for the positive side and black for the negative side, is attached to each post with a large clamp. A hold-down clamp keeps the battery in its place while driving.


The following recommended battery maintenance steps should be followed for ANY car, old or new. For our classics, which are driven much more infrequently, these checks are even more critical, and will help ensure that your collector car battery is always up to the task of starting the engine and letting you take your buggy out for a spin.

  • Check the electrolyte

If you have a flooded cell battery, remove the battery caps and check the water level at least twice a year. I recommend spring and fall; every three months is even better. The electrolyte level should reach the top of the ‘ring’ so that the level looks like an oval. USE DISTILLED, NOT TAP, WATER. Buy a jug of it at ShopRite for 89 cents and keep it in the garage. Don’t overfill the battery. If you accidentally overfill and cause a spill, wipe it up with paper towels (wear gloves to avoid acid burns; even the mild electrolyte solution can sting) and discard the towels.

If the battery frequently needs topping up, the case may be cracked. Check along the sides and bottom for signs of corrosion from spilled electrolyte; a cracked case cannot be repaired. If the same cell is always low and all the others are OK, that cell may have sulfated; you may need to replace the battery.

  • Clean the battery top

I began my career working on fuel-injected Volvos, which is where I learned that a dirty battery top (covered with dust, grease, oil, whatever) can cause current flow between the positive and negative posts. The resultant voltage loss is enough to disrupt the electronic fuel injection. Cleaning the battery top would sometimes fix a poorly-running car!

Since then, I’ve been fanatic about ensuring that my cars’ battery tops are clean. One tried-and-true method is with a solution of baking soda and water. If it’s not too dirty, any mild cleaner might do. I’ve used Windex, Brakleen, or Simple Green. You don’t need a lot; again, use paper towels, wear gloves, and throw the towels away. The goal is a clean, and dry, battery top.

Note the start of corrosion at base of terminal clamp
  • Tighten the battery hold-down

On a rally many years ago, I was driving my ’68 Mustang while following a friend who was in his Austin-Healey. He hustled it at speed around a corner, immediately after which, it stalled. Dead. No crank, no nothing. I pulled up behind him to assist. By this time, he had the hood open, and it was obvious to me that the battery wasn’t there. “Ron, where’s the battery?” I asked. He replied “in the trunk”. We both saw it as soon as the trunk lid was popped: during the tight right-hander, the unsecured battery flopped over, yanking the negative cable clear off its post at the same time.

You may or may not be rallying your car, but the battery is supposed to remain securely in place. All cars have some sort of battery hold-down. Check yours. If it’s missing, replace it. If it’s loose, tighten it (but not too tight, which could crack the case). By the way, bungee cords are a poor substitute; purchase a proper hold-down. Ron and I both thank you.

  • Clean and tighten the posts and cable terminals

This one is the most important maintenance tip, and it’s also a very neglected one. We will get into electrical flow in a future article, but suffice to state that for your car’s electrical system to deliver peak performance, all connections must be clean and tight.

Battery terminals build up corrosion for a number of reasons: engine compartment dirt, arcing from dissimilar metals, electrolyte seepage. Whatever the cause, this corrosion will interfere with consistent electrical flow out of the battery and to all the electrical devices in your car. It is imperative to clean and tighten these connections on a regular basis.

Simple battery maintenance tools and supplies: petroleum jelly, brushes, dielectric grease

Start by removing both battery terminals. ON A NEGATIVE GROUND SYSTEM, ALWAYS REMOVE THE NEGATIVE CABLE FIRST, AND REINSTALL IT LAST. This will prevent possible short circuits at a ‘live’ positive terminal. Clean the battery post and both inside and outside of the cable terminals with a stiff brush (you can pick up steel or brass-bristled brushes for about a buck apiece). Use a cleaning solvent as recommended above.

REINSTALL THE POSITIVE CABLE FIRST, THEN THE NEGATIVE CABLE. Clamp them tight, then smear petroleum jelly or dielectric grease on the terminal tops. The aftermarket offers plastic “battery terminal toppers” which snap on top of the terminals. If your engine compartment is particularly messy, consider these as extra protection. They provide the added benefit of helping to prevent accidental short-circuits.

Topping up the electrolyte, washing the battery top, and cleaning and tightening the terminals are all simple maintenance steps that any vehicle owner can accomplish. Even if you’ve never wrenched on your own car before, you can do this!






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