First, if you plan to do any work to your bike you need to disconnect the battery so you don’t accidentally create a short, burn your wiring or engage the starter and lose a finger. I didn’t plan on giving welding lessons in this article so be sure to disconnect the battery before doing any work! Always disconnect the negative cable first. The negative cable is grounded to the frame, so if you accidentally touch the frame or any metal nothing bad will happen. If you disconnect the positive side first and accidentally touch the frame or metal you are creating a ground which will let the juice run right through you, maybe start a fire, just not good any way you look at it.
To disconnect the negative cable on the battery you’ll need that trusty 10mm wrench. Make sure when you disconnect the positive cable it won’t touch anything metal, like the frame. I usually stick a shop rag or a short piece of rubber hose around the terminal to be sure it doesn’t make contact. If you maintain your battery properly from the beginning you should be able to get 3-5 years out of it.
Let’s talk about inspecting the battery. First the battery contains electrolyte which is a sulfuric acid solution that can do some damage to your skin and eyes. One of my lucky jobs here at my shop is filling and charging batteries. I’ve had the acid spill on my clothes and lost several pairs of jeans to battery acid. Trust me you don’t want this stuff on you or anything else, so please wear eye protection and gloves when handling the battery. It’s nasty. Keep it clear of other chemicals, the welder, concrete, steel, heat or open electricity. This goes for batteries, also. Evil items.
Most of the newer bikes come with sealed batteries making it almost impossible for the acid to spill out, but nonetheless you should always be cautious. When installing a new battery it must be charged fully to insure a long life. Follow the instructions included with the new battery on how to charge it initially. The newer sealed-type batteries have different charging instructions than the earlier wet-cell types. If you fill your battery and just give it a quick charge because you’re in a hurry, the second you hit the start button, and put a load on the battery, you just guaranteed yourself a short battery life. If the battery wasn’t charged correctly initially it will never be able to be charged fully. So like anything in life, slow down, take your time and do it right.
Inspecting the battery and charging system
The top of the battery should be clean from dirt and residue. If the cables and terminals have any oxidation or corrosion you will need to clean them with a wire brush or a piece of sandpaper. Protect your eyes. Check all the fasteners for tightness and any breakage. Look at the battery posts to make sure they haven’t warped from overheating. Basically, look the whole battery over for cracks, leaks, loose terminals, burned connectors or terminals and swelling.
If your bike won’t start and it seems the battery is dead, you need a voltmeter, quick. You’ll use to test the voltage of the battery. More often than not, you’ll find that checking the cables for loose terminals, corrosion, frayed ends or worn insulation leading to a short is more than likely the culprit of the dead battery. Also check grounds. A rusty, bad-connection ground will prevent charging and drain your battery. If you don’t have a voltmeter, check battery terminals, wire connections, fuses and sand your grounds. If nothing makes a difference, call your local shop to get your bike in for an appointment. Have the shop do a voltage test for you.
”Yes bad grounds,” Sara added when I spoke to her, “ especially with a custom built bike. A lot of guys, going at it for the first time, don't realize you need to tape off the paint or powder coat where the engine and trans will be mounted. They also need to shave the finish away where ground cables mount.”
A voltmeter has limitations, since it can’t measure the overall strength of the battery, like a load producing amp gauge. But you can determine if the charging system is working. A battery should have 12.9 volts at idle. To test the charging system rev the bike, get the RPMS up to about 2500, and the gauge should indicate close to 14.5 volts. If your gauge moves up at all then the charging system on your bike is working. If the reading on the voltmeter doesn’t move up, it’s time to test your charging components, the regulator or alternator.
Charging System
I want to explain a little about the motorcycle charging system. Basically there are two charging system set-ups on American V-twin bikes. The early style charging systems consisted of the battery, generator and a mechanical regulator. The generator created a direct current (DC). The regulator maintained the proper voltage to the battery and all other electrical units such as lights, Ignition, etc. The regulator, did just that it regulated a constant voltage unaffected by engine speed or load.
If for some reason you find yourself getting into to the charging system on a generator type bike and disconnect the battery, then the generator is going to need to be polarized before starting the engine again. If you don’t polarize the generator first, the charging system will work in the opposite manner and actually drain the battery voltage instead of maintaining or “regulating” it. Please refer to your service manual if you find yourself in need of charging system care and polarizing info.
On later style bikes, usually 1978 and up the charging systems consists of the battery, voltage regulator and alternator (stator and rotor). The alternator is made up of the rotor, which is mounted on the engine sprocket shaft, and the stator you’ll find bolted to the crankcase. The rotor, which contains magnets, spins with the crank around the solid-mounted stator. The stator is a group of copper wound coils. The rotor spinning around the stator creates an alternating (AC) current of approximately 30 to 50 volts. This current flows to a solid-state voltage rectifier/regulator. The regulator converts the AC current to DC volts (direct current), your battery requires. This unit also limits (regulates) the output it sends.
If the charging system on your bike is causing problems the first place to start is at the battery. Again you’ll check and clean battery terminals, cables, grounds, wire connectors and fuses. After checking, cleaning and re-testing, you may need to inspect and test the charging system components. Refer to your service manual for all correct procedures, if you want to perform the tasks yourself.
A very common problem with charging systems is the alternator/voltage regulator wire plug pulling out away from the stator plug. Take two seconds to check that the voltage regulator plug is fully inserted in the stator plug and clean (Located on the forward side of your primary cover). You can purchase voltage regulator retaining clips to hold that plug from backing out—good idea. Or make a custom one. Nature of the beast, vibration will shake things loose on a Harley. Again, test the charging at the battery with the voltmeter. If it doesn’t increase from 12 volts, you can test the alternator by reading AC volts. If it’s working, check the regulator connections. If they are cool the regulator is shot. If the Alternator is not putting out, it’s shot. Replace it, plug in the regulator and check again. The regulator may also need replacing, maybe not. Make sure to check the magnets on the rotor. Also don’t bang the rotor onto the engine main shaft with a hammer. You could knock a magnet loose.
Coils
Let me tell you a little bit about the coil. The coil is basically a transformer. It transforms the 12 volts from the battery into higher voltage and sends to the spark plugs. Inside The coil there are 2 “coils” or windings, a primary and secondary with a laminated iron core. This is all sealed in a watertight insulating compound. If tests show the coil is bad it is not something you can rebuild or repair, you must replace it. Your service manual will go into detailed explanations on how the ignition systems work on V-twin engines. Please refer to that section of the service manual for more in depth information.
A great safe and easy way to maintain the life of your battery is with a Battery Tender. It’s a charger that monitors the condition of your battery. It will charge the battery for you and keep your battery fully charged, prolonging cell life. When you hook the battery charger to the battery, red is for positive and black is for negative. Your tender will tell you when the battery is fully charged.
I recommend taking the battery off the bike to charge it. If the battery overcharges, it can overflow, and the acid will destroy paint, chrome and wiring. If you’re using a motorcycle Battery Tender, you won’t have to worry about overcharging. The Battery Tender shuts off automatically. Make sure the charger is turned off before you hook the battery up to it, same thing when disconnecting. Unplug the charger before removing the connectors.
If you do take the battery out of the bike, the positive gets disconnected last when removing and connected first when re-installing. Make sure you refer to your service manual before attempting battery removal.
NOTE. Always disconnect the negative cable first when removing, and connect the negative cable last when re-installing.
