To start off with, I am not going to attempt to explain the workings of a Virago battery from the chemical standpoint For those who really want to know, there are plenty of books and internet sites that describe the innards of a lead acid battery, and the chemical reactions that make it work.
But in order to talk about battery functions, we do need to get into a little nuclear physics. First, let's understand that some smart guys a while back decided that everything is made up of atoms. (That's another reason why you love your bike so much. Both you and your bike are just a bunch of atoms!) Atoms are made up of particles such as protons, neutrons, and electrons. It's those electrons we are interested in, since when they start moving they make what we are after, electrical current. Some atoms have a tight relationship with their electrons. The electrons stay at home in the atom and don't go wandering around. (Those electrons make good husbands/wives) But some atoms have electrons that can be easily busted loose to wander off to hook up with other atoms. These are called "free electrons" and when they get moving from one atom to another they become "electricity" or electrical current.
Materials made up of atoms with few or no "free" electrons are called "insulators" because their electrons can't be easily budged out of the atoms, and nothing can flow.
Materials made up of atoms with plenty of "free" electrons are called "conductors" since electrons can be easily popped loose to jump to the next atom down the line.
Normally atoms have the same number of protons and electrons, which keeps them nice and comfortable with no electrical charge. However, where an atom loses one or more electrons, it becomes known as a positively charged ion. Its protons remain the same in number and so it is now out of balance on the positive side. It yearns to pick up its lost electrons from somewhere to get back into balance.
On the other hand, where an atom is forced to play host to one or more extra electrons, it has more electrons than protons and is called a negatively charged ion. It would love to get rid of these extras so it can relax again.
Now that we are all clear on nuclear physics, let's talk about batteries. Lead acid batteries are basically made up of plates which in turn are made up of negatively and and positively charged ions. Between these plates sits a fluid--electrolyte. Thus batteries are capable of storing up excess free electrons in its negative plates and pushing them out through a conductor over to the positive positive plates. When a conductor is connected between these two sets of plates, a chemical reaction occurs in the battery which gives us a flow of electrons (current), and in the process we get electrical power ("electricity") to run our lights, run our ignition, etc.
If this process continues long enough without recharging the battery, the amount of current flow diminishes and will eventually peter out completely. We motorcycle riders won't be happy because our batteries are now "dead". But the battery will be happy because it has got rid of all of all those excess free electrons on the negative plates and sent them to the positive plates that didn't have enough.
Charging a battery basically produces chemical changes which allow the battery to store the excess free electrons it needs to give us some current. In other words, charging "force feeds" more free electrons into the negative side of the battery than it really wants, and it is now ready to spit those back out at the first opportunity, that is, the presence of a conductor to take them away over to the positive side that is is starving for them.
The strength of the "push" behind those free electrons is measured in volts. The more volts, the greater the pressure on those free electrons to move out through a conducting circuit. All Virago batteries are rated at 12 volts. Early vehicles came with 6 volt batteries. A 12 volt battery can be thought of as twice as "hot" as a 6 volt battery, that is twice as much push behind the electrical current.
O.K., let's get practical.
TWO KINDS OF BATTERIES
When you walk into your auto Parts store you will see two different kinds of batteries. The most common are "Starter" batteries. These batteries are designed to give a "burst" of power for short periods of time in order to drive your starter. Then they like to sit back at (or close to) full charge, and let your generating system do the work of running you lights, ignition, etc. Starter batteries do not like to be deeply discharged.
The other common type of battery is the "deep cycle" battery. These are designed to give sustained power for longer periods in order to run golf carts, wheel chairs and other michines that don't have an active charging system at work. They can be discharged much deeper than starter batteries, and still recover many times upon recharging.
When we talk about Virago batteries, we are talking strictly about Starter batteries.
ROLE OF THE CHARGING SYSTEM
When the engine is running, we have a charging system working in the bike which is tied into the Virago battery circuit and also generates current to run the lights, etc. This charging system can create this current at a slightly higher voltage, say 14 volts, than the voltage found in the battery, say 12+ volts. The effect of this is that if the battery is low in charge, the higher voltage produced by the charging system will force feed electrons back into the battery to bring it to full charge, in addition to running lights, etc.
An electrical device in the circuit called the "voltage regulator" keeps things in balance here, assuring that the lights, etc.get what they need, and that the battery gets recharged after the discharge due to starting, or the drain at low rpm levels, where the charging system is not putting out enough to run everything, and the battery is discharging to make up the difference.
TYPES AND POWER RATINGS OF VIRAGO BATTERIES.
Virago batteries come in last two different sizes. The 920, 1000 and 1100 models have batteries that measure roughly 8 X 6.5 X 3.5 inches. 700 and 750 batteries are slightly thinner. The battery fitted to the 1982 Virago 920 J had a special sensor in it to warn of low battery acid levels. NOTE: The battery box in '84 and up 700's and 750's has a foam spacer in it to make the thinner battery fit snugly. If you want to install the larger size battery in those models, you can do so by removing this spacer.
Batteries are rated in volts, but another common rating tells how much power they can deliver on a sustained basis, say over a 10 hour period before they are fully discharged. Power is measured in terms of amperes ("amps") which is a measurement for how much current is flowing. So the total power of Virago batteries is measured in Amp/hours or Ah. A 15 Ah Virago battery can provide a steady 1.5 amp current for 10 hours before the battery is fully discharged. Virago batteries (all 12 volt) are rated as follows:
920's (all) 20 Ah
700's, 750's 16 Ah
1000's, 1100's 20 Ah
Why bigger batteries in the bigger bikes? They are all 12 volts, right? Well, in general, the bigger the physical size of the battery, the longer the battery can provide sustained power, especially when faced with a heavy load, like the power needed to turn the starter. You've noted that thick starter cable, no doubt. That is designed to accept about all the power the battery has without getting hot and melting. So with somewhat more compression resistance by those bigger pistons in 920's, 1000's, and 1100's Yamaha decided to add a little bit of extra capacity for the bigger engines. Call it extra "cranking power".
"Cranking power" is another common measurement for batteries, but Yamaha doesn't give us ratings here. I would estimate that the typical Virago battery can deliver somewhere around 200 "cold cranking amps", that is, cranking amps measured at O degrees Fahrenheit.
RESISTANCE IN THE CONDUCTING PATH
One other concept which is good to know is this: The amount of current (amps) which flows from your battery is controlled not by the battery or battery size, but by the amount of resistance in the conducting path. Put a conductor between the temrinals, and you get all the power the battery can give, which will be enough to create major sparks and melt tools and wire. Throw substantial resistance in the path, such as a bulb, and you get a much smaller and controlled flow, basically only enough flow (amps) to light the bulb.
But note that when starting the bike, the resistance in the the starter circuit is very low, and the cables (and frame) are big, fat conductors. So we get a high burst of energy, and current gets to flow at close to maximum. It is not good to subject the starter to prolonged starting sessions, because all this current can heat it up to where solder starts melting here and there and the starter motor may destroy itself. Which brings up to--
JUMPING YOUR BIKE FROM CAR BATTERIES.
Yes, we know, it is still only 12 volts. But that big car battery will be able to deliver perhaps twice as many cranking amps (or more) than your motorcycle battery. And since resistance is low in the starter circuit, you are likely to get a bigger burst of power than from your motorcycle battery. So the car battery is potentially capable of doing damage that a smaller MC battery wouldn't do, particularly if your bike isn't starting readily and you keep at it too long. Also, if the engine of the car is running, the actual voltage available maybe a lot higher than the 12+ volts you need to run your ignition and can possibly damage electronic components.
Have I ever jumped a bike from a car? Well, yes. In an emergency that may be your only alternative. But be sure the car engine is off. And if your bike doesn't start readily and it looks like you are facing a long, hard session on the starter, consider pulling out your MTS card, and having them pick you up. Maybe cheaper than the alternative.
Another point about jumping. BE SURE THAT YOU HAVE YOUR CABLES ON CORRECTLY. Plus on plus, ground on ground. If you attach your cables backwards by mistake (it isn't that hard to do as I can relate to you from personal experience) and particularly if you have your ignition turned to run your starter, electrical components in your bike can be damaged. The proper procedure is to attach the positive cable to the battery terminal first, and then the negative terminal to the frame somewhere away from the battery. This avoids any sparks near the battery. (The battery produces explosive gasses, particularly when charging. They do explode on occasion as many mechanics can attest to from personal experience.
A final point is that with later Viragos, access to the positive terminal of your battery isn't that easy, and so you'll need to pull your battery out most of the way to jump it. Don't try hooking jumper cables to small wires. They will just fry when all those cranking amps hit them. I suppose jumping directly to the starter may be possible, but I can't recommend it. Your ignition system may also need those 12 volts to start and run the bike.
MEASURING THE CONDITION OF YOUR VIRAGO BATTERY
There are three ways that I know of to do this:
1. Measuring the weight (specific gravity) of the fluid in your battery. For our purposes we need only to understand that as a battery becomes fully charged, the fluid in the battery becomes heavier as the sulphur content in the electrolyte goes up. Thus if the "specific gravity" is measured at 1.28, this indicates a fully charged battery. At around 1.08 the battery can be considered fully discharged, or dead. Small hydrometers for motorcycle batteries are easy to find at motorcycle dealers and accessory houses. The downside of this method is that you have to gain access your filler caps to take these measurements, and with '84 and up bikes, this means removing the battery. Also, this method is obviously not available to you with sealed batteries, which are becoming more and more available for Viragos, and represent a "better mousetrap", though more expensive.
A note here on battery removal in later Viragos. I get e-mails from guys who say, "I pull and pull but my battery won't come out." Solution: pull harder, or find a friend who can. Also you can help the battery clear the frame if it is binding. A good trick is to use one of those clamps with soft, broad jaws to grab the battery and wrestle it out. You cannot read the fluid levels in the cells of your wet battery with the battery in the bike. So do the right thing, and take it out periodically to check those levels and top them up to the upper line if needed. You can use your hydrometer as a filler syringe--distilled water only, please.
2. A second method which is, in my opinion, a good and easy one for most owners, is to simply measure the voltage across the Virago battery terminals with a common, inexpensive digital multimeter, set to measure DC volts. A brand new, fully charged battery, should be able to RETAIN about 12.6 volts (sealed AGM batteries, slightly higher). The concept of "retain" is key here. Put a charger on a motorcycle battery and charge the battery "fully" as indicated by lights on the charger. Pull off the charger and take a reading. Most likely you will see somewhere in the 13 volt range. Now let the battery sit for a few hours, say overnight, and take another reading. The "surface charge" voltage will have gone away and the battery will have settled down to the voltage it can "retain" on a continuing basis. This is the voltage we are interested in.
Note that there are three ways your Virago battery can lose voltage:
a. "Using" the battery (lighting a light) will allow those excess electrons to flow, and will lower the voltage. Recharging will restore it. A "use" you need to be aware of is what is called "parasitic discharge" that is, the small amount of power that is used by any clocks, alarms systems, etc. that continue to take power from the battery when the bike is not running.
b. When a battery is just sitting it will "self-discharge", as power slowly leaks out. This leakage is normal and very slow, and can be made back up by charging.
c. As time marches on, the plate materials in the battery deteriorate through a process called "sulphation", as well as heat, and vibration. As they degrade, their ability to retain power goes down. So at some point the initial "full charge" voltage of 12.6 can no longer be maintained and battery will be on the "slippery slope" toward its demise.
3. A third method of testing requires more expensive equipment and involves putting a load on the Virago battery and then measuring its ability to rebound. Your dealer or motorcycle shop may have one of these testers, and you can take your battery in and have it checked.
Assuming your charging system is working well, you can also run these voltage tests after you've had the bike out for a ride. Let it rest a bit before testing.
BUT NOTE: These tests can be unreliable on damaged or abused batteries. I've measured good voltage on batteries with internal shorts, that actually had no power whatsoever. Also if you have let your electrolyte go very low and have to top up with major amounts of distilled water, hydrometer measurements may not be correct. I have seen good hydrometer measurements and poor voltage measurements (and vice versa) in the same battery.
TRICK: On later Viragos, with the battery in the bike, the positive terminal is out of reach. Next time you have the battery out, make a little pig tail with a spade connector which will run out from the positive terminal. It can be a small wire, and you can solder the loose end and put a small screw cap on it. That way you'll have access to both the positive and negative terminal without removing the battery, and can check voltage easily. You can also use this wire with motorcycle rated chargers. many of these chargers come with ready-made pigtails that can also be used.
1. The first thing to do is get off to a good start. When putting a battery into service yourself, carefully follow the directions that come with it. Or buy a battery from a dealer or shop that knows what they are doing and pays attention to initial charging requirements.
2. Battery fluid (electrolyte) levels will go down over time due to heat, and charging. Check and top up this fluid periodically using DISTILLED WATER ONLY. Tap water may contain minerals that will shorten the life of your battery.
Note that battery fluid will start to boil off if charging continues on a fully charged battery. If your battery keeps going low on fluid, check your charging system for overcharging. Also heat can cause evaporation and a loss of battery fluid. So if you are considering a free way run of hundreds of miles through the desert at 110 degrees, be sure your fluid is topped up before you go, and maybe check it afterward. If the fluid drops below the top of the plates your battery will lose its ability to function fully and the dreaded "sulphation will occur.
3. Don't let your battery get seriously discharged. As noted above, "deep cycle" batteries can rebound from being close to fully discharged. Motorcycle batteries are not "deep cycle" batteries. I would recommend that you buy one of several motorcycle battery chargers that charge at a sufficiently low rate (.5 to 1.5 amps) so that the battery will not get hot from too high a current. Good ones also have a built-in voltage regulator which will stop the charging when the battery reaches full charge, and go into a maintenance mode, at a very low voltage level, to cover self discharge and/or parasitic discharging. As noted above, most of these chargers come with pig tails that you can mount permanently to you battery, so you can easily plug in the charger when you are not using your bike, and also use that pigtail to take voltage measurements
The main problem with over charging is that the plates and other materials in the battery get so hot that they actually disintegrate to where the mechanical and chemical structure of the battery is destroyed. Motorcycle chargers mainly range from .5 amp, to 1.5 amps, which means that the battery is charged (force fed) slowly, causing a minimum of heating. Using a car battery charger of say 6 amps, is going to throw too much current at your battery too fast, and will heat it and hurt it.
Motorcycle batteries don't give much problem in and of themselves. If a battery won't stay charged you are often looking at a charging system problem rather than a battery problem. While batteries do wear out and must be replaced, I've seen batteries last 3-4 years, and longer in motorcycles where they were properly maintained.
However there is one problem that can occasionally bite you and that is the internal short. Probably due to the vibration that these batteries are subjected too, the insulation between those negative and positive plates can sometimes break down and allow a major short in the battery. That is, those excess electrons can now find their way to the starved plates without leaving the battery. When this happens things go totally dead on the bike. The infuriating thing here is that sometimes the battery will do this intermittently. You turn the key on and things seem normal. You hit the starter button and things go completely dead. The other trap here is that if you are checking voltage, your voltage may read 12.6, that is normal. So if you suddenly experience a catastrophic electrical failure on your bike, don't overlook this possibility. A quick check is to simply jump the terminals on your battery. You may see a voltage reading of 12+ volts, but if the battery is internally shorted, the jumper wire won't give you more than the wimpiest little spark.
There are two big ones Battery acid is acid and not to be gotten into eyes, on your skin, or on clothes. Read safety directions that come with batteries, and take normal safety precautions. Also, the vapours produced in batteries (particularly during charging) are flammable. I have never seen a battery blow up, but I have a friend who had one blow up on him. No sparks, flames, or smoking around Virago batteries.
A NOTE ON MAINTENANCE FREE BATTERIES
Maintenance-free batteries are available at least for later model Viragos. Yuasa offers them and others may too. They function basically as described in this article, but the chemistry inside them is different. No more topping up battery fluid or measuring specific gravity with a hydrometer. After the initial fill of electrolyte (battery acid) they are sealed, and you never go into them again. They weigh more than standard batteries and are said to be more robust. They retain a slightly higher voltage than standard batteries--maybe 12.8 volts, and are said to provide more cold cranking power. They are also more expensive. How much longer they might last, I can't say from personal experience, but their ability to retain specific gravity (due to slower electron leakage) is said to be much greater.
The Yuasa maintenance free sealed battery has a updated number: YTX24HL-BS. The battery comes dry with a special filler container full of electrolyte. I would say that if you can read directions, are reasonable handy, and reasonably careful, you can handle the task of loading this battery yourself. You should be equipped to do the initial charge per the instructions.
Want to go through life having a pleasant and rewarding battery experience?
1. Get your Virago battery off to a good start by following the filling and charging instructions that come with it, or assuring that these things are done right by the dealer.
2 Buy a good quality motorcycle battery charger with a "maintenance" mode, attach the pigtails to your battery, and plug the charger in whenever you are not using the bike on a daily (or very regular) basis. Don't let your battery sit for long at less than full charge. Your battery loves to stay fully charged at all times.
3. On wet cell batteries, check fluid levels periodically. More in hot weather.
4. Measure the voltage across the terminals of you battery periodically to check your "retained" voltage.
5. Replace your battery if signs of decline develop.
6. Consider buying a new battery every 3-5 years whether you think you need one or not.