One of the most feared aspects of car repair, maintenance, or even a restoration is the vehicle's electrical system. Watts, volts, ohms, and other terms swirl around most people's heads like sharks circling a bleeding surfer, and at the heart of that electrical system is one of the most misunderstood parts--the battery. In our Mustangs, be it vintage or late-model, the starting and charging system is based on a 12-volt negative ground service, so we're not going to bother with six-volt or positive ground systems for this story.
As the heart of your electrical system, your battery, must not only be able to start your Mustang by supplying enough power to the starter, but it also must be able to provide auxiliary power for key on and key off accessories (when the engine is not running and therefore the alternator not supplying the vehicle's power, for things like listening to the radio or the interior lights illuminating when the doors are opened). Lastly, the battery must be able to store this power between vehicle use (but not long-term storage) so that the car will start the next time you use it.
So why is it that this most important part of your electrical system is so often just left to fend for itself and never given maintenance until that fateful day when you get up early to head out to a car show and you find your Mustang in the garage with a dead battery? Your club members are meeting for the drive to the show in 20 minutes and you're standing there with the hood up wondering what you should do.
Taking care of your battery is really a simple process. It is something you need to add to your regular maintenance schedule. You check your engine's oil level on a regular basis right? You need to check your battery's level on a regular basis too. Keeping your battery properly charged not only means you'll be able to hop in and twist the key when you need it most, but the battery will last longer and save you money. Of course, there are a few preventive measures you can perform on your battery as well, and we'll go over those as well.
Batteries do not last forever. They should be considered a consumable item. That being said, sometimes it is best to start off with a new battery if your battery is of a questionable history. Just bought a classic Mustang and there's no real indication of the battery's age? You might want to play it safe and simply buy a new battery. Depending upon location, you can often guestimate how close you are to needing a replacement battery. In hot climates like Florida, Arizona, and Texas, you're probably going to see three years max out of a high-quality battery.
Today's batteries are typically a sealed, maintenance-free design, so there's little you can do to service the battery except for keeping the terminals clean. Often an "eye" on the battery will tell you its condition. If your battery does have removable service caps to allow checking the battery's level, then you should check the level at regular intervals. Be sure to remove all jewelry before servicing your battery and wear eye and hand protection. Remove the caps and check the fluid level. The fluid level should allow for the battery's lead plates to be completely submersed. If not, you can carefully add distilled water to bring the level back up.
If you own and know how to use a hydrometer, you can also check the specific gravity of your cells if the caps are removable. The same can be said for the battery's open circuit voltage (measured across the terminals). If you own a volt-meter, you can check the voltage too. Use the above chart to determine your battery's state of charge.
Finally, external condition is just as important as the internal condition. Case damage, terminal damage, and more should all be things to look for on a regular basis. Of course, if your battery is properly secured, there's little chance of external damage, but we've seen cases nicked when being dropped into place, so be careful and don't rush things when installing your battery.
The previous two batteries...
The previous two batteries are lead acid flooded batteries, meaning their case is essentially a plastic box with fluid that floods the battery’s lead plates. There are other battery types, including gel-cell and AGM, or absorbent glass mat. Probably the most popular AGM battery is the Optima, which uses spiral cell technology where the lead plates are tightly wound into a cylinder form and sandwiched with the absorbent mat that holds the electrolyte and prevents it from spilling. The Optima battery is sealed and there is nothing to really do maintenance-wise save for keeping the connections clean and tight and ensuring the battery is charged.
This "maintenance free" battery...
This "maintenance free" battery actually has removable vent caps. If you're not sure if your caps can be removed, a bit of gentle prying with a small flat-blade screwdriver should help determine if they are removable or not. The terminals are in great shape on this battery and there's no case damage, but we do see some terminal corrosion that needs to be taken care of; more on that later.
We frequently get tech questions...
We frequently get tech questions from readers about what's the best Optima battery for their application. Optima has tech bulletins, tips, and more on their website where you can find answers to many of the questions. However, answering the "right one for me" question is fairly simple. Optima offers three main battery types, all denoted by colored tops--RedTop, YellowTop, and BlueTop. The BlueTop is designed for marine use, so we can rule that one out for Mustangs. The RedTop is a cranking or starting battery, so it should be considered if your primary concern is starting the car, no matter the temperature or starting demands. The YellowTop has cranking power similar to the RedTop, but also features deep cycling capability, which means it can support demanding electrical loads like big audio systems, high key-off electrical loads, and so forth. The YellowTop can "bounce back" from being deeply discharged without damage, unlike conventional batteries.
In our opinion, the first...
In our opinion, the first thing this battery needs is a shot of flat black paint, but we'll worry about that later. You might have noticed that the battery is not retained in the tray. Many modern battery case designs, even though they are listed as Group 24F, do not have the proper hold-down ridges molded into the case, but we have a fix for that we'll show you a bit later. This battery has raised vent caps that are removable for checking fluid levels, and the posts are quite dirty.
Here's that unsecured yellow...
Here's that unsecured yellow case battery in a '66 Mustang battery tray and the solution--a conversion battery tray (PN 10732-1C) from National Parts Depot. Available for $14.95, the tray requires the use of the '67-'70 style retaining rods and hold-down bracket (PN 10756-1K and PN 10718-2A, respectively). The tray bolts in place of the stock tray using the stock tray's fasteners.
One side benefit of the new...
One side benefit of the new tray design is that without the side hold-down clamp, the tray is shortened to meet the case side wall, leaving a couple of inches of space for a larger radiator, fan shroud, wiring, or anything else that might have been in the way with the stock wider tray with side clamp.
Something else to consider,...
Something else to consider, especially for those using flooded batteries, is an anti-corrosion mat. NPD stocks them under PN 954-1A for under five bucks. You simply cut it to fit your tray and place it under the battery. If your battery leaks or over flows from overcharging, the mat will absorb the battery's electrolyte and minimize damage to the battery try and fender apron. That's cheap insurance in our books!
With our flat top, maintenance-free...
With our flat top, maintenance-free battery back in place, we decided to give it a more correct look with NPD's Autolite Sta-Ful battery cover. These plastic covers drop right over a Group 24 flat-top battery and include separate vent caps (so you can position them any way you like) and a positive terminal post warning tag like the originals.
A nice detailing touch is...
A nice detailing touch is a correct set of battery cables. Not only are these cables made for the application, thus being the proper length with the proper end sizes, they add a nice touch of originality to a Mustang. When you order battery cables, you'll get a positive and negative battery cable, plus the starter cable. You should inspect your cables regularly and replace them as a complete set if any need replacing. We also recommend the standard red for positive and black for negative, especially if you're buying parts store replacements, so that helpful person won't blow up your battery while trying to jump start your Mustang.