The battery is the heart of the electric system of a motorcycle. It is an electrical component that stores and supplies the electricity required by the on-board electrical system. A high-quality battery and proper battery maintenance ensure years of operation and optimal performance of the motorcycle. Actually, it should be called accumulator because it is rechargeable, unlike a battery. However, the term battery has prevailed.

The vast majority of today's motorcycles have a sealed, maintenance-free unit. However, if you own an old motorcycle, the situation may not yet be so comfortable that you can simply plug in the motorcycle battery and drive off.

Did you know that there are batteries with different power ratings? Their unit is the Ampere Hour, Ah? How do the terminal blocks work? How to charge a conventional battery? All these questions probably go through your mind...

In this article, we will cover the basic questions you might have about your motorcycle battery. How to charge your motorcycle battery, you can also read in this guide.

Where is motorcycle battery located?

Different motorcycle manufacturers hide battery in different places. If you have a motorcycle manual or owner's guide, you will find the exact location there. If you haven't received a parts list or a manual with your bike, you will certainly find it on the Internet. There are either pdf copies available or parts lists viewable at many large retailers or online forums.

In general, in most cases, the battery is located under the seat. It can also be behind the side covers, or under the fuel tank. But in some instances, it can be in the rear section of your bike, especially if it is a modified custom model.

Is motorcycle battery 12v or 6v?

Depending on when was your motorcycle manufactured. Motorcycles manufactured in the late fifties and early sixties had primitive electric systems and therefore only needed 6V. Also, older off-road motorcycles had no electrical accessories, so some may still run on 6V batteries. As the requirements for the motorcycles changed, more functions were added. The battery technology has also evolved and the 12V AGM standard battery became a norm (AGM Definition: Absorbent Glass Material).

Typically, 12V batteries provide an advantage over older 6V batteries. They supply only half the current (Amps) of a 6 volt system, giving fewer resistance effects in the old wiring looms and rusted connections. Having a 12V battery in your motorcycle means that you have a better choice of bulbs and other electrical accessories (including horns, indicators, LED bulb conversions, etc).

Explaining the Ohm'slaw: 

For electrical conductors, the voltage U that drops above the conductor is proportional to the strength I of the current flowing through the conductor. This proportionality is called OHM's law and is described by the equation U=R⋅I.

U is the voltage in volts, R is the resistance in ohms and I is the current in amperes.

If the formula is changed to resistance, the result is as follows:

R= U/I

12 Ohm = 12 Volt / 1 Ampere but also

12 ohms = 6 volts / 0.5 amps

In conclusion: With the same resistance, you can only use a lamp with a current of 0.5 amps. The lamp has a lower luminosity.

Even if your machine is built for 6V batteries, not all is lost. There are conversion systems available on the market, such as solid-state electronic voltage regulators.

Inspecting the condition of a vintage battery

If your motorbike has been sitting for a long period of time, the chances are that the battery is flat. Before you start any work on it, you should inspect its condition first.

The best way to assess the condition of an old battery is to remove it from your bike. When disconnecting it, always remove the negative terminal (black clamp) first. This way you can prevent any potential sparks to earth as you undo the positive terminal (usually red clamp). You can then proceed with a visual inspection.

Check the state of the terminals. Are they broken, bent or damaged? Since the content is a dangerous acid, check the battery case for any cracks or leaks.

When working on batteries, the following principles apply:

Wear safety glasses and work gloves.

Avoid any skin and eye contact.

Next is to ensure that the inside of the battery is sound. If you can see through the box, check for any signs of deterioration of the lead plates, such as grey or white areas. This could mean the battery has reached the end of its life and might not be worth charging.

Finally, check the liquid levels within. If you are certain that the battery box is not leaking, you can top the level with distilled water to the correct level. Remember, the vapours are highly flammable, so ensure you are in a well ventilated area, and you turn off any potential sources of heat or flame.

Is a vintage motorcycle battery rechargeable?

Yes and no, that depends on the condition of your battery. Both 6V & 12V batteries can be charged if in good nick. Vintage and classic motorcycle batteries naturally tend to discharge when not used for an extended period of time. Once they lose their charge, they are prone to cracking and freezing, especially in the winter months.

If you are not sure about the state of your battery then you should go to a specialist workshop. They can run professional tests and also charge it for you. This can be cheaper than buying an expensive device for a few charging processes.

Bike batteries come in two types: Wet cell lead-acid batteries and sealed MF lead-acid batteries. Both types are in essence plastic boxes full of highly corrosive acid. So handle with caution!

Wet cell batteries were made for vintage cars and classic motorcycles. They work on the base of liquid electrolyte solution and require manual topping off with distilled water. Never use tap water or any acids! However, over time the electrolyte inside will run out, and you will need to buy a new battery. These batteries release highly flammable gasses during recharging and manipulation. As such, they are pretty much obsolete.

A conventional battery (MF lead-acid) does not require such topping up and has enough electrolyte to last for a long time. It will still require maintenance, but that is much simpler and less hazardous.

How to charge a motorcycle battery?

If your vintage battery is not showing any signs of damage, the lead plates seem functional and the levels of liquid is topped up, you can charge it and test it. Motorcycle battery tends to be more delicate compare to average car battery, if you charge it too fast, you can ruin it. So investing in a good quality battery tender (charger) is a key.

Choosing the right motorcycle battery charger

There are two main parameters to consider when buying a charger (or so called battery tender). First one is the voltage, if you have a 6-Volt battery, you need 6V battery charger, if you have a 12V, you need a 12V one. As explained earlier, the 12V is more common, but always check the top of the battery or the owner's manual to ensure you buy the correct charger.

The second thing to look for is the Amps (the ampere number). The higher the amperage count, the faster you can charge it. Every battery has manufacturer's recommended amp hours stamped on the case. If you can't find it, you should charge it at no more than 1/10 of its amperage rating. For example, if your battery rating states 10 amps, you should only charge it 1 amp per hour for 10 hours.

The last aspect of battery charger is the type of battery you have. There are different motorcycle chargers for lead-acid and different ones for lithium batteries.

Smart chargers

The easiest way to charge a motorcycle battery is using a smart charger. This clever piece of kit will detect the state of your battery and automatically modify the charge to its needs. You don't need to worry about overcharging your battery with a smart charger. Smart chargers monitor the charge levels to keep them at an optimal level even over long periods of time.

Trickle charger (Standard charger)

These are standard battery chargers that can be used for a variety of appliances. They produce a constant current until unplugged, so there is a risk of a battery overcharge. When using a trickle charger, you'll need to monitor the charging process closely.

You will also have to ensure, that you disconnect the charger once it is fully charged. This may take half a day or few hours, depending on your battery. It is best to use a timer! Most trickle chargers have a light that displays when the battery is fully topped up.

Charging motorcycle battery made easy

Connect the charger to the battery with the leads supplied. Make sure you connect the negative port of the charger to the negative terminal (black wire), and the positive port of the charger to the positive terminal (red wire).

Plug the charger in and turn it on. If you are using a trickle charger, check if the battery is charging and start your timer. You will have to monitor the charging process and disconnect it as soon as it is fully charged. Avoid days of charging!

If you are using a smart charger, you can just leave it plugged in until you need the battery again. Most todays chargers have an indicator that will tell you when the battery charged.

When disconnecting the battery, ensure you switch the charger off first before detaching any of the cables. Then you should disconnect the negative cable first and the positive cable as last.

Partial charging is just as harmful as overcharging. Remember that a battery that has not been used will need to be charged every 30 days.

Safety precaustions when charging motorcycle battery

NEVER CHARGE A BATTERY WITHOUT FIRST REVIEWING THE INSTRUCTION MANUAL OF THE CHARGER YOU ARE USING. In addition to the charger manufacturer's instructions, you should follow the following safety instructions:

Always wear appropriate goggles and protect your face and hands in an appropriate way.

Charge batteries only in well-ventilated rooms.

Set the charger to OFF before connecting the connection cables to the battery to avoid dangerous sparks.

Never attempt to charge an apparently damaged or frozen battery

Connect the charger's connection cables to the battery. Connect the red cable (+) to the positive (+) pole of the battery and the black cable (–) to the negative (–) terminal of the battery.

Make sure the connection cables are not broken, worn or loose.

Set the timer, turn on the charger and slowly increase the charging rate until the desired current (A) is reached.

If the battery gets hot, outgassing violently or splashes electrolyte, reduce the charging rate or temporarily turn off the charger.

Always set the charger to OFF before removing the connection cables from the battery to avoid dangerous sparks.

Do lead-acid batteries have a 'charging memory'?

Lead-acid batteries have a phenomenon known as 'charging memory'. It means that they refuse to accept a charge higher than the one they have experienced. The way to get past this phenomenon is to keep batteries fully charged using a smart charger. You will not be able to fully charge a battery that suffered from charging memory. It is irreparable damage. If that happens to your battery, you will have to replace it.

Will motorcycle battery freeze?

An old-fashioned motorcycle battery contains distilled water. Therefore freezing temperatures can be a problem. Most modern motorcycle batteries use gel. They are designed to work on as low as -18 degrees. However, it may be difficult for the battery to deliver a constant current at freezing temperatures.

On the other hand, extremely high temperatures can take a toll on your battery life as well. Protect your motorcycle in an appropriate form and avoid extreme temperatures.

How do I maintain battery terminals?

Acid and copper sulfate can accumulate on battery terminals and cause damage to them. This reduces the terminals' contact area, limits the supplied current, and makes it difficult to charge a battery properly. The corrosion caused by the acid can cause high electrical resistance, which makes it harder to start a battery. The battery terminals can be cleaned with a simple stiff toothbrush alongside rinsing with water. Most importantly, ensure that the battery is disconnected before you proceed with any maintenance.

What's the difference between gel battery or AGM battery?

Gel batteries are often confused with AGM batteries. What distinguishes them and what do the batteries have in common? Both types of battery belong to the VRLA batteries and are equipped with a pressure relief valve. The abbreviation VRLA stands for Valve Regulated Lead Acid Battery. With this closed battery type, the hydrogen produced by the battery is recombined – the refilling of distilled water as with wet batteries is omitted. Apart from these similarities, there are significant differences between the gel battery and the AGM battery.

The gel battery

A gel battery is similar in structure to a conventional wet battery – positive and negative electrodes are surrounded by an electrolyte. As the name suggests, the electrolyte is not in liquid form, but is put into a gel-like state by the addition of silica. This results in greater insensitivity to vibrations and vehicle position. The encapsulated design facilitates handling and improves safety – if the battery is intact, the user does not have to fear leakage of liquid. A gel battery is therefore often referred to by the trade as a maintenance-free battery. 

The AGM battery

With the AGM battery, the electrolyte is completely bound into a glass fiber fleece. The AGM battery is leak-proof and can easily withstand inclined positions. This and the susceptibility to vibrations are reasons why the AGM battery has many trailers, especially in the off-road and two-wheeler sector. Compared to a conventional starter battery, an AGM battery can handle three times the number of charging cycles. The performance advantage achieved by design features is one of the main arguments for the use of an AGM battery. Long service life, outstanding performance and high safety make the AGM battery a premium battery for modern vehicles.

In conclusion

Vintage motorcycles batteries differ from their modern counterparts. However, you don't have to have a vintage battery to run your classic motorcycle. If you want to stick to the old fashioned acid-lead battery for authenticity, you need to follow certain rules and caution. Just keep in mind that regardless how well you look after the old battery, it will never be as reliable as a modern equivalent.

It isn't difficult to charge a motorcycle battery, you just need to follow few simple rules as mentioned above. With the help of smart chargers, a flat battery will never be a worry for you again.

One last tip: 

A battery cannot be charged by letting the motorcycle run idle for a while. Most motorcycle engines don't generate enough power when idling to actually recharge the battery. Charging at idle does exactly the opposite, the battery is discharged even more!

Follow these advices when caring for your motorcycle battery. 

The Sumo Rubber Team wishes you a long lasting battery and good ride!

Amy Saunders
Amy Saunders
Sunday 27th February 2022

Hi there! Guess what? My father-in-law just won a contest organized by a local supermarket, in which the grand prize is a brand new moped! Hence, thank you very much for making me realize that extreme temperatures can largely influence the fluidity of the substances inside our motorcycle battery. This kind of makes me thinks of my sister who's been developing some kind of interest towards superbike lately. I think she should know about this article so she can take good care of such vehicle later.

Wednesday 02nd March 2022

Hello Amy, thank you for your comment,. However I'm a little surprised that you didn't know these things since you are promoting a battery charger website?

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