Classic Car Battery System Guide

Everything You Need To Know About Charging Systems

By Ryan Manson   –   Photography By The Author

A properly charged and maintained battery is a must for any classic car, but especially so when it comes to those equipped with all mod cons like EFI, digital gauges, A/C, and more. The more advanced the component, the more sensitive they seem to be to a steady, reliable 12V signal. Many systems, in fact, will cease to operate properly if provided with anything south of 11 V. That leaves a small margin of error when it comes to the alternator providing steady charge under normal driving conditions or to the battery itself if left to sit idle for too long a period. Leaving a trickle charger attached to that hot rod with an expectant slumber of a period over a week or so has become common practice.

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Read More: ‘57 Ford Ranchero Dual-Purpose Hot Rod

Charge System Considerations

But before we can even worry about proper maintenance of the battery and charging system, we need to be sure that the system’s wiring and cables are properly sized, fabricated, and run safely across the vehicle to further ensure the system’s reliability and performance. Long runs of battery and charging cables need to be sized properly, securely terminated, and properly protected.

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02 New Duralast Platinum AGM battery installed in a 1932 Ford roadster
We replaced an old, tired box in a recently resurrected 1932 Ford roadster with a new Duralast Platinum AGM battery. The mounting location behind the seat made for limited options due to the size constraints, but we were still able to find a unit capable of 540 cranking amps in the relatively small Group 51R confines, thanks to the vast Duralast line.

Charging Cable Length & Gauge Size

As lengths increase, so does diameter size to overcome the resulting resistance in said wire/cable. For example, a 10-gauge wire on a 30-amp circuit has an acceptable run of around 10 feet. Extend the run of that wire another 2 feet and the size requirement jumps to 8-gauge. The longer the wire, the more resistance in the wire, hence the larger size to make up the disparity. Now, this is based on a rough set of specifications related to wire temp and percentage of acceptable voltage drop.

03 Properly sized battery and charging cables in a 1955 Chevy trunk
Properly sized battery and charging cables are very important to a reliable charging/power system. Here, we’ve made a set of 1/0-gauge wires to relocate a battery to the trunk area of a 1955 Chevy. These cables will run from the battery, to a remote disconnect solenoid, and then onto the starter.

Battery Relocation Considerations

A wire that runs through the passenger compartment will see more moderate temps than one that runs from the engine compartment and alongside the exhaust, so other factors need to be considered as well, all based on individual circumstances. Like many things in the hot rod world, these are baselines and not hard and fast rules. Suffice it to say, when in doubt, run a larger-gauge wire.

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Read More: How To Fix Quarter Panel Rust

04 Assembly of custom battery cables using a Summit Racing Battery Cable End Crimper
Making custom batteries and charging cables isn’t difficult, given the proper tools. Here, we’re using a Battery Cable End Crimper from Summit Racing (PN KYS-10068859) to assemble the previous set of cables. Good connectors, a solid crimp, and protective heat shrink tubing is the key.

Ground System

Getting power to the component however is only half the battle. Once there, the current needs to pass through the load and make its way back to the source (the negative terminal on the battery) to complete the electrical circuit. That’s where the ground wire comes into play. Every component on your vehicle has a ground circuit, but some are more obvious than others. Many have a separate ground wire that will connect to either the steel body or chassis or directly back to the battery itself. Others may use a point of contact (housing, mounting screw, and so on) that connect the ground side of the circuit to the body/chassis.

05 200 amp midi fuse for battery circuit protection
Proper protection of the various circuits, be it to/from the alternator or the fuse panel, is good practice. Here, a 200-amp midi fuse will be used between the battery and the alternator/fuse panel feed.

Tips For Chassis Grounds

Regardless of how this circuit may be connected, they all need to route back to the battery without interruption. This is why it’s imperative to have clean grounding straps between the battery/frame, frame/body, frame/engine, and so on. In fact, it is even better to run a complete grounded circuit that all the components can attach to that doesn’t require a perfect bond between an eyelet connector and a painted/powder coated chassis, for example. As we mentioned earlier, a number of modern components can be very sensitive to proper ground connections, especially when it comes to EFI sensors and other precision equipment, making the case for a good ground even more important.

06 Battery cables safely routed through sheet metal panels using Summit Racing bulkhead connectors
Routing big battery cables through sheet metal panels can be a tricky affair but can be done safely by using bulkhead connectors such as these items from Summit Racing (PN SUM-CSUMG1431).

Read More: Hemi Swapped 1932 Ford Roadster

The foundation for that foolproof charging system comes down to a few simple points. Size the wire correctly and make clean, secure connections, including the grounding circuit. Do this and you should never find yourself stranded, at least not for lack of trying! MR

07 Safe battery cable routing using a protective grommet
Of course, if it can’t be done using that method, use of a grommet to protect the wire is a must.
08 Insulated clamps used for secure cable routing along frame rail
Down the frame rail, proper support of both cables is a must using insulated clamps, routed as such that they can’t risk rubbing against anything and are well clear of any potential heat source.

09 Properly routed battery cables clear of heat sources

10 Painless Performance Products engine body ground strap kit for optimal grounding
Good grounds are absolutely a necessity and this engine/body ground strap kit from Painless Performance Products (PN 40140) is a perfect start to linking all the components back to the ground side of the battery.
11 Main ground connection to the battery body and engine securely attached to the chassis
Here, the main ground going back to the battery is on the left and connects to the body grounding wire at right and the engine grounding strap, all while attaching firmly to the chassis.
12 American Autowire All Copper Grounding Kit for a trouble free grounding system
Taking the grounding game further, American Autowire offers an All-Copper Grounding Kit (PN 500717) that eliminates the reliance on the chassis as a grounding component and effectively links all the components in the wiring system together and directly to the battery for a trouble-free grounding system.
13 Powermaster Performance alternator with properly sized positive and negative wires for optimal performance
The goal of all this is to develop a battery/charging system that provides all the power possible to run all those components successfully and reliably. The alternator being a big part in this system, it’s imperative that the wiring for the alternator is not undersized for not only the positive side of things, but for the grounding side as well. A Powermaster Performance alternator has been equipped with two 4GA wires, one on the positive side (with the boot) and one on the negative side (at the stud). The addition of a proper ground wire can increase the alternator’s output and performance, but it must be sized accordingly (i.e., same as the positive cable).


American Autowire
(800) 482-9473

Clampdown Competition


Painless Performance Products
(800) 423-9696

Powermaster Performance
(630) 957-4019

Summit Racing
(800) 230-3030

Click on this issue’s cover to see the enhanced digital version of Battery Basics and Beyond!

mr december 2023

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