t best our hot rods are driven infrequently and clearly not as much as we would like. For many the winter climate precludes a number of us from driving these cars at all, at least until the fair-weather season. As such, keeping our cars in running order begins with a fully charged battery. A simple and fundamental thought, but to do this we need to understand some basics, such as our car’s battery, battery chargers (maintainers), and battery parasitic loss (draw).

To better understand what it takes to keep our hot rod “at the ready,” let’s take a look at the Optima chargers, batteries, and one hot rodder’s experience with parasitic loss … me! I found myself gaining a greater understanding through insight as to the problems, the cause, and the correction(s).

I have my Optima Digital 400 charger attached to my roadster year-round. It never lets me down and the roadster is always at the ready. I now have three hot rods (1972 Suburban, 1968 Corvette, and 1929 Ford highboy roadster) that are running that I like to drive as often as possible. And, they all need battery maintenance. But there’s more to this electrical puzzle than just keeping your battery fully charged.

The Optima Digital 1200 charger is ideally suited for charging batteries other chargers can’t, will charge faster than other units (often with twice the output), it won’t overcharge your battery, and will maximize your battery’s performance. The Optima Digital 400 (most common among hot rodders) has a feature that will maximize battery life and performance with its built-in battery health mode. It will also recover discharged batteries other battery chargers/maintainers can’t and will keep all 12V AGM (Absorbed Gas Mat, which is a type of lead-acid battery) and flooded batteries (features battery acid covering all internal parts) at a healthy charge during storage.

Whether your hot rod battery is on a charger or not there’s something called parasitic battery drain (or draw). This means your car is drawing power from the battery even though your ignition key is in the “off” position. Because the key is “off” doesn’t mean there aren’t accessories that are still drawing current. And, guess what, that’s exactly what I was experiencing with my roadster … and Suburban and Corvette!

How do I know this? Well, I had the roadster out for a weekend romp and was intending on driving it again the next day but magazine deadlines have a way of dislodging the best laid plans of even the most seasoned (old) editors. I parked the roadster and forgot to hook up the Optima 400. Nearly three weeks go by and when I go to start the roadster there was the proverbial “nothing.” I achieved nothing but finger/wrist exercise by turning the ignition key with no, nothing, nada results. I knew everything was in good operating order, including my Optima battery when I parked it. What happened?

In short order, after attaching my Optima charger the roadster started and all was good for the day’s drive, but I was still curious about what was happening. I’m aware of parasitic battery drain, or draw, and knew that there had to be a reason causing the drain, such as the modern electronic accessories that increase the draw. After attaching the test equipment (digital multimeter), I noted that I was losing 180mA over a 24-hour period, which is a higher draw than I expected, given the lack of accessories, or so I thought. Based on this, my battery would have drained itself in approximately 10 days. Typically, new cars are set up to last to somewhere between the 21- to 40-day range without intermediate charging.

Here’s the math that I used to determine what happened to me at a 180-milliamp draw over 24 hours (0.180 x 24 hours = 4.32 amps per day). Now my battery is a 44Ah battery/4.32 amps per day = 10.185 days before the battery is at a 0 percent state of charge. (Zero percent state of charge is reflected in a battery status of 10.5 V, which will not start your hot rod. And for those with electronic fuel injection the voltage demands are higher than, say, a carb-equipped car. Upside, the Optima chargers will bring such a battery quickly back to “life”.) All of this is under the assumption that the battery was fully charged at the time but odds say unless you have taken your car directly off of a charger it isn’t fully charged. Also, heat (ambient temperature where the battery is housed) can exacerbate the loss of potency, while cooler temperatures can slow down the drain.

It’s typical to expect at least 0.05 amps of power draw when the vehicle ignition is “off.” A clock in the radio draws as little as 0.01 amps, whereas the combined interior lights can exceed 1 amp. Doesn’t sound like much, but a single dome light can pull enough power to drain a battery in one day. Remember, it doesn’t have to take your battery to zero overnight, just low enough for it not to start. Did you know that a key fob, common on new cars, used in your hot rod is capable of dragging your battery down while “asleep” in your garage? It’s constantly searching. Even your Classic Instruments SkyDrive (GPS) speedo/odometer has a normal draw of 0.06 amps (60 milliamps). There are other accessories, such as the channel memory feature in your car’s stereo, that also have a continual draw. You begin to add up all of the “vampire” accessories your hot rod has and you can see that there’s a draw going on all the time.

Of course you can always remove the battery from the car and place it in a safe location and it will last for months (assuming it is fully charged when it was removed). This leads us to a modern-day myth (although once it was true) that leaving your battery on a cement floor will cause it to drain more rapidly. There was a time that was true but the Optima battery, because of the material used in its case, will not allow this to occur. Frankly, the real reason a battery dies is from sitting. A battery will drain no matter where you place it; that’s what batteries do.

Optima will tell you that should you drive your hot rod (or any car) regularly so it can still benefit from being attached to a charger at least once a month to keep it fully charged. What’s fully charged? According to Optima the battery should register at least 12.6 V. Should the battery drop below 12.4 V a sulfation process begins, which in turn lessens the life of your battery. For us hot rodders who drive our cars intermittently, it’s a good idea to leave the charger on continuously during storage.

Of course, there’s one way to get around the continual draw on your battery and that’s to install a disconnect (kill) switch, such as the Flaming River model shown in the photos. This will allow your battery (assuming it’s in good condition) to last for a significantly longer period of time. There are some instances where accessories are wired to circumnavigate the kill switch, such as alarm systems, and they can range from 21mA to 43mA draw. Other draws that can be present, even with kill switches, revolve around how you have wired your car’s stereo system. It’s possible that your stereo system, in order to maintain its channel memory, will have a minimal draw (0.03 amps or 30 milliamps) in order to maintain its memory. You may also need to install a relay switch so that the stereo doesn’t draw power from the battery when it’s “off,” but this is typically for the simple “on” and “off” power wire. (A note on relay switches. If they are stuck in the “on” position, this can lead to a battery drain. Also, alternators with bad diodes can cause battery drain.)

Which battery will suit your needs? There are a number of factors that go into this decision process, such as cold cranking amps (CCA) and the amp hour (Ah), to handle the number of accessories that draw power when the ignition is in the “off” position. High-compression engines or cold-weather conditions require that batteries have this extra CCA power. Should your car have a number of vampire accessories then the Ah is important to you.

Then there’s the hot rodder’s packaging (fitment) dilemma … “What will fit the area that I have to work with?” While this is a real (and serious) decision, oftentimes this shouldn’t be the basis for a battery. While the physical size is a real concern (not so much weight), the CCA can usually be addressed but proper Ah or RC (reserve capacity) generally comes up short. It’s in these instances that the continual use of a charger in between use is of the utmost importance.

For the purpose of this story we are addressing two of the three common Optima batteries, the RedTop and the YellowTop (we will ignore the marine BlueTop).

RedTop is designed for engine starting where an alternator immediately monitors the state of charge and provides energy to the battery whenever it is needed. For a street rod with average electrical demands, this is the battery to use.

YellowTop is designed for deep-cycle use and the electrical loads are higher than average, or when the discharge cycle is more than typical engine starting, such as vehicles without alternators. This also includes racing vehicles without a charging system, cars with audio/video applications with large electrical demands.

I must say that I have four Optima batteries in use, with two being RedTop and two being YellowTop. Given my use and the true number of accessories and driving demands I could get along just fine with all RedTop. But alas, when rummaging around the tech center to replace a tired battery I grabbed what was available (again, not really the way to make a battery decision).

We’ve all heard the expression, “It’s the little things …” The truth couldn’t ring truer when it comes to maintaining your car’s electrical charge. Something as insignificant as a few amps of parasitic draw can lead to problems if you aren’t on guard and prepared to protect your battery.

13 Here we see that the LED readout signifies that the battery is 50 percent charged and the charger is suppling 3.8 amps while the battery is registering 12.8 V. The battery has ample charge to start car.

14 Harbor Freight offers these digital multimeters that are ideal for performing simple electrical tasks throughout your hot rod.

15 Harbor Freight also offers jumper cables and these should always be in the trunk of any car you are driving. Might help yourself or a friend in an emergency.

16 Classic Performance Products offers battery boxes and hold downs. This one is ideally suited for this SPIRALCELL (precisely wound “Jelly Roll”) Optima battery with top and side terminals.

17 From Hot Rods by Dean is this Optima (Group 34) battery hold down that has the kill switch built in.

18 Called “The Big Switch” battery disconnect from Flaming River, it has an easy-to-use handle for “on” and “off” positions, comes with its own mounting bracket and hardware, and has a watertight seal.

19, 20 There will always be electrical connections in hot rods and this one from PerTronix is ideal … a Weather Pack Sealed Connector Wiring Kit. Include this kit with a pair of rubber-handled wire connector crimpers and you are set.