Battery Fitment/Detailing
Having the properly sized battery for your Mustang is just as important as having the proper capacity. Generally speaking, using the battery group as originally specified by Ford is the easiest way to ensure things go smoothly. If your Mustang uses a Group 24F, don't use a Group 58, and so forth. Problems like terminals on the wrong end of the case, cases too wide or too tall (hitting the hood of the car or the inner fender), or simply the footprint of the case being too large for the battery tray are all issues that can be solved by simply using the proper battery group for your application. There are still companies that make the proper battery cases for our vintage Mustangs; you just have to look for them. However, they are getting harder to find.
One solution for '65-'66 owners is to update the battery tray to a conversion tray that uses the '67-'70 style hold-down assembly. While not correct for concours use, it is a solid and safe solution that bolts right in and cost less than $30. For those who can find the correct battery group, try to purchase a flat top, maintenance-free battery and then you'll be able to use an Autolite replica battery cover that slips over the battery posts and makes your universal battery look like a correct Autolite.
Maintaining your battery means ensuring it is properly charged as well as taking care of the battery's fluid level, connections, and exterior condition during the months you use your Mustang. All you need is a few simple tools to keep your battery's connections in proper working order. As we said before, add your battery to your list of regular maintenance items or get in the habit of checking the condition monthly, or perhaps at each oil change (especially for those daily drivers out there).
Charging a discharged or sulfated battery is a simple process, but it is imperative that the proper charging equipment and safety procedures be followed. Standard flooded batteries are much more susceptible to sulfation of the lead plates. This limits the battery's performance and can cause a no-start or lack of charging. Modern battery chargers and maintainers have a de-sulfation mode that helps break down these sulfates and put new life into older batteries. Look for a quality charger/maintainer that has multiple battery type settings so you'll only need to purchase one product no matter what type of battery you are charging.
Lastly, never consider your car's alternator as a battery charger. If your battery has died from leaving the lights on or other roadside issue, you should really charge the battery fully before starting the car, versus jump starting it and then driving the car to charge the battery. We've all done it, especially in an emergency, but the best case scenario is to have a friend or family member bring out another battery and charge the dead one properly at home.
AGM batteries can be a bit tricky, as they have different considerations for charging. Older 12-volt chargers will usually only charge an AGM type battery to approximately 80 percent, which is why we again recommend a newer charger/maintainer that has an AGM setting. AGM batteries, like flooded batteries, do well with a lower amperage charge (1-10amps). Charging at higher rates generates a lot of heat, which reduces battery life. AGM batteries are most known for not "taking" a charge if they are deeply discharged, often meaning below 10.5-volts at rest. If your AGM battery is drained below 10.5-volts, you'll need to charge it either by using an AGM specific charger or by connecting the discharged AGM battery in parallel with a good battery so that the traditional charger "sees" the good battery and charges appropriately.
| Voltage | Approximate State-of-Charge at 80°F Average Specific Gravity |
| 12.65 | 100 percent | 1.265 |
| 12.45 | 75 percent | 1.225 |
| 12.24 | 50 percent | 1.190 |
| 12.06 | 25 percent | 1.155 |
| 11.89 or less | Discharged | 1.120 or less |  Hopefully you've got a battery...  Hopefully you've got a battery post/terminal brush in your tool box. If not, there's no excuse not to have one, as they run just a few bucks at any auto parts store. This is your number one tool for post/terminal maintenance. They quickly and easily clean the terminals for the best connection.  Once you've removed a battery...  Once you've removed a battery terminal from the battery post, it is often difficult to reinstall the terminal over the post due to the distortion of the terminal clamp (usually caused by over tightening). A battery terminal spreader simply allows for a quick and safe way of spreading the terminal open enough for it to fully seat around the battery post. Then the terminal can be tightened properly to retain it to the post. If you find you're having trouble removing the terminals in the first place, a terminal puller is another tool you can look into for removing the terminal easily from the post.  Our cleaned battery post is...  Our cleaned battery post is ready to accept our battery cable. As you can see, the post's surface is clean of any accumulated corrosion or dirt and the surface is spotless.  Just as important as the main...  Just as important as the main battery cables is the engine ground cable. Because the engine sits on rubber isolators, it does not inherently have good grounding capabilities for sending units, ignition, charging system, and more. A simple ground strap from the back of the engine to the firewall is what Ford has used for decades and it works well. Again, a concours-type ground strap like this one from NPD means it will be the right length with the proper eyelets for your application. Don’t forget it, especially those doing engine swaps, as it’s easy to leave it on the old engine.  The same tool can be used...  The same tool can be used to clean battery cable terminals as well. Just remove the protective cap and twist the brush into the cable terminal to clean the surface.  While not 100 percent necessary,...  While not 100 percent necessary, we rarely need an excuse to buy new tools, right? So hit the tool store for a set of terminal pliers and a terminal spreader. These tools will help remove and install your cable ends without damaging them or your battery posts.  The terminal pliers are designed...  The terminal pliers are designed to grab the square head of the terminal pinch bolt and hold it while you remove the threaded retaining nut. If you've ever dealt with a soft terminal and a spinning pinch bolt, you'll know why they invented these pliers. They hold the bolt securely and prevent it from spinning and damaging the terminal.  Optima has recently released...  Optima has recently released their very own charging solution, the Optima Digital 1200 charger. Designed to maximize the Optima AGM battery's condition, the charger can also be used on traditional flooded batteries. It features a digital charge gauge that shows all connection types, warnings, and state of charge messages as the charger goes through its six-step charging/maintaining process. The charge leads feature built in LED work lights for connecting to batteries in dark locations such as a trunk mounted battery. The charger also features a USB charging jack for cell phones and other small devices.  If long term storage is common...  If long term storage is common for your Mustang, a battery terminal disconnect switch like this one from NPD (PN 957-3) is a simple solution. It even comes with a small fused jumper wire to maintain your aftermarket radio's memory while still preventing major discharge from leaving the lights on or a door open. We still recommend a battery maintainer be connected, but this switch reduces the amount of time the maintainer is needed.  We've owned this CTEK battery...  We've owned this CTEK battery charger/maintainer for about four years. The Multi US 3300 is a slim unit that can be used on flooded batteries or AGM batteries just by selecting the battery type on the face of the unit. It has a quick connect feature so you can use permanently mounted ring terminals or the typical spring clamps.  If your AGM battery falls...  If your AGM battery falls below 10.5-volts open-circuit voltage, a standard charger might not recharge the battery. While we recommend a modern charger with an AGM circuit built into it, if you're in a pinch with a standard charger you can simply connect a known good battery in parallel (positive to positive, negative to negative) and then connect the charger to the cables directly as shown. This will allow the charger recognize the voltage of the good battery and start providing a charge. Maintain this charging connection until the open-circuit voltage increases above 10.5-volts, then you can remove the second battery and jumper cables.  CTEK's latest model is the...  CTEK's latest model is the MUS 4.3, which has an eight step charging/reconditioning process that can solve many battery problems, including deeply discharged flooded batteries, sulfated batteries needing reconditioning, AGM specific charging, a winter charging mode, and more. Like all CTEK chargers, the connections are spark proof, reverse polarity protected, and short-circuit proof. You can literally clip the clamp on leads together and nothing happens. No sparks, no arcing, no blown fuses. Try that with your old bench top charger.
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