Classic Car Batteries: Your Frequently Asked Questions Answered

Jul 27, 2010

Though often forgotten about, the battery is what keeps all of a car’s nifty electrical parts charged and running. Daryl Brockman of Optima Batteries answers some of the most-common tech questions his customers have regarding batteries for their classic cars.

Q: Which battery should I install?

A: The question they should be asking is ‘How much battery do I need?’ If you plan on adding a lot of electronics, then you want a battery with deep-cycle capability. A starting battery is designed to crank the starter briefly and then be fully charged again by the alternator soon afterward, whereas a deep-cycle battery will be much more tolerant of being drained repeatedly. [Will your customer] be running their stereo at a car show without running the engine? Do they idle along at a cruise with the air conditioning and electric fans running? Using a deep-cycle battery is important in these situations, although a lot of people don’t realize it.

Q: How can I mount/install a battery so that it looks completely stock in a traditional restoration I’m doing?

A: The restoration people, depending on how hard core they are, don’t even want to modify how the battery is held down. They don’t even want to drill holes in the battery tray to accommodate a slightly different sized battery. Some will want to add modern conveniences and then hide the necessarily larger battery.

There are several manufacturers- (we’re not affiliated with any of them) [that] make cases for disguising a modern battery or even specifically for hiding an Optima battery.

For example, Quail Services of Corona, California, makes a case that disguises an Optima six-volt as a period-authentic six-volt. Another company called Tar Topper [in Phoenix] offers a variety of vintage-look covers for Optima and other modern batteries.

Q: What are my options if the project vehicle doesn’t need to look completely stock?

A: Rodders who are less-concerned about a traditional appearance can hide an Optima battery or even mount it on its side. If you tilt a conventional flooded battery, then the liquid acid inside is going to spill out all over the place. But Optima uses Absorbed Glass Mat (AGM) technology where the acid is held in suspension, more like the liquid in a sponge. That gives you a lot of flexibility to tuck the battery away where the OEM never intended.

Q: What about venting?

A: A regular flooded battery will vent a small amount of gas under normal use, that’s just the way they work. Under normal use an Optima battery will not vent gas, but if it’s overcharged a relief valve will open to release some internal pressure. Those fumes are both toxic and flammable. [Particularly if the battery is mounted in the passenger compartment, Optima recommends mounting it so that any gas that comes out can easily escape.]

Q: How much cable does a remote battery require? What kind of gauge does it need?

A: The most-common consideration when you are moving the battery from under the hood to anywhere else is that you are probably moving it farther from the engine. As a result, you’ll need a higher-gauge cable so that electrical power can still be transmitted to the engine over that distance. There are charts on the Internet that can tell you the right cable [to use]. If you want a bullet-proof installation, we recommend 00 welding cable. Use that and there will be no question that you will have enough current capacity.

Q: How can I keep a battery fully charged in a car that I plan to store for awhile?

A: [A maintenance charger] gives you a margin for error if, say, you forget to turn off the lights. Some maintenance chargers have a desulfation mode that will help recondition the battery as long as it’s connected. [Keep in mind that an unused battery will discharge faster in warmer weather.] If you live in Phoenix or [Miami] or Los Angeles, your battery will go flat faster than it will here in Milwaukee.