When it comes to choosing the best battery for your motorcycle it’s not as simple as you might think; from wet lead-acid to AGM and lithium, they all have their benefits and pit-falls. And how should you look after them?
Originally from South Africa, Martin’s based at the Canadian design centre where, among his many regional and global management roles, he also conceptualises new TecMate products. Oh, and he’s still very much a keen motorcyclist…
Martin Human was the design engineer of the first ever OptiMate
What do the numbers mean on a motorcycle battery?
There are two really useful numbers to look out for. The first is Ah (amp hours), which tells you how many hours a battery will last when something is drawing 1A from it. So a 10Ah battery can supply 1 Amp for 10 hours or 2A for 5 hours. Or 5A for 2 hours and so on; basically it shows you the capacity of the battery.
The higher Ah number, the longer a battery will last.
The other handy number is the Cold Cranking Amps (CCA). You need plenty of power to start an engine – especially a big V-twin – and CCA reveals the number of amps the battery can supply at a temperature of -18°C for 30 seconds without dropping below 7.2 volts. The bigger the engine, the more CCA you need.
Did you know… the symbol for amps is always a capital ‘A’ as it’s named after André-Marie Ampère. The same goes for volts thanks to Allessandro Volta
Lead acid batteries have been around since the middle of the 19th century and all work the same way.
Without turning this into a chemistry lesson, a normal 12V lead-acid motorcycle battery is made up of a plastic case containing six ‘cells’. Each cell is made up of a set of lead ‘plates’ – lead for the negative plate and lead-oxide for the positive plate – which are immersed in a sulphuric acid and water solution called ‘electrolyte’. The biggest difference between different lead acid batteries is how that sulphuric acid is stored in the battery.
In a standard ‘wet cell’ battery it’s in liquid form, essentially sloshing around inside. When charging, the chemical reaction generates some hydrogen and oxygen from the chemical components of water (H2O) in the electrolyte, which escapes the battery. That’s why you need to top up with distilled water on occasion.
In a sealed AGM (absorbed glass mat) battery – the most popular in current motorcycles – the electrolyte is suspended in fibreglass mats between the plates; the mats are basically sponges that have soaked up the acid and keep it directly in touch with the plates.
The sulphuric acid content in the electrolyte is much higher, which is why this type of battery can generate more power, and it’s filled once then permanently sealed. A recombination chamber within the top of the battery allows the hydrogen and oxygen generated during charging to condense into droplets that feed back into the mats. In a perfect world it’s a totally closed system, but there is a valve that will open if the pressure inside exceeds a safe level, typically when the battery is grossly overcharged (higher than 15V), hence the term VRLA or Valve Regulating Lead-acid. These batteries can be safely mounted on their side.
Then there are GEL batteries, and I only mention them as many motorcyclists confuse GEL with AGM. Even though they’re both sealed VRLA batteries, they’re designed for quite different uses. In a GEL battery the electrolyte is mixed with a gel substance making it so thick it will not easily leak out, but that also slows down electrical ion movement. So GEL batteries work great where constant power is needed – like in your home alarm system – but not as starter batteries.
AGM is the best lead-acid starter battery.
Did you know… batteries are made up of multiple cells. For instance, a single 1.5V AA is, technically, a cell. Put more than one together though, and they become a ‘battery’. A typical motorcycle lead-acid battery is made up of six cells, each producing 2V.
Firstly, an electrical circuit in a motorcycle is pretty much a closed circle of electrically conductive materials, all containing electrical ions that are the workhorses of electricity. Those electrical ions carry energy given to them by the chemical reaction inside the battery or the motorcycle’s charging system.
In your motorcycle engine the active component that makes it run is gasoline combined with air; that fuel explodes within a controlled space (the cylinder), pushes down the piston and ultimately causes the wheels to turn. Twist the throttle and you go faster, but you also burn fuel faster.
In a lead-acid battery that ‘fuel’ is the sulphuric acid mix (electrolyte). However, a battery cannot shut off – its chemical process varies between really slow idling to maximum rated power, usually delivered during starting of the engine.
Sulphate molecules from the sulphuric acid combine with the lead atoms from the plates to provide energy to the electrical carriers, which take it wherever there’s an electrical path to travel, passing it on to atoms that demand it from them.
Within the battery they mostly idle along between positive to negative plates and very little energy is spent doing that, but the instant you turn on an external circuit connected to battery posts (like the headlamp), everything speeds up; those electrons have somewhere else to go, carrying and delivering their energy to willing recipients (atoms), circulating back and repeating until the battery has nothing left to give.
The battery is completely discharged when the sulphuric acid (H2SO4) in the electrolyte has been depleted of all sulphate molecules, with the result that the electrolyte is now basically water and there’s a whole lot of lead-sulphate atoms crowded around the surfaces of the plates.
Just like a running engine generates ‘waste’ chemicals that are expelled out of the exhaust, within the lead-acid battery, lead-sulphate atoms are generated as ‘waste’. But the good news is that the lead-sulphate ‘waste’ remains within the battery and better still, it can be completely recycled.
During recharging the process is reversed, the electrical ions in the circuit receiving their energy externally and carrying it back into the battery, splitting the lead-sulphate atoms, causing them to break up into their original form, with the lead atoms remaining at the plates and the sulphate atoms being shuttled ‘home’ to the electrolyte to strengthen the ‘fuel’.
Once all the waste lead-sulphate has been broken up the battery’s ‘fuel’ is regenerated.
In your motorcycle’s electrical system it’s a give-and-take scenario; the battery gives energy when the system (via the alternator) cannot, usually during starting and idling, but when the engine is running at a good pace the system gives back to the battery.
A lead-acid battery is a great regenerative power source that can continue to give its rated power if you always recharge it completely, soon after discharge, essentially breaking up every single lead-sulphate atom inside the discharged battery and converting it back to acid. A bad side effect of not doing so, even partially, is that those lead-sulphate atoms bond together (crystallize) and form a non-electrical film on the surface of the lead plates, making it difficult for electrical ions to pass through and even more difficult to split them up.
This is known as sulphation – the battery is sulphated – and it will usually prevent the battery from fully recharging (or holding a current for any time), unless you use a specialist charger like the OptiMate 4, which can desulphate a battery (break up the crystallized lead-sulphate) and recover its ability to receive and hold charge again.
That moment when you turn the key and get nothing except some dash lights and a click can be easily avoided…
As explained above, a battery’s chemical process is never-ending. It cannot be turned off. So when not used it sits there idling, but so slowly it will take many months for it to completely lose charge. It’s easily preventable with a smart charger that keeps it topped up aby delivering energy to counter that discharge within.
Depending on the quality, a bike battery could last anything from a few weeks to several years, depending how it's treated. On average, we’d expect to see three to four years before performance tails off, but a well-maintained battery that’s hooked up to a smart charger when the bike’s not in use could easily double that.
For most batteries, not keeping them adequately charged – allowing lead-sulphate to build up to a point where that battery cannot function as designed – is what makes it unable to receive or hold charge.
The worst combination is allowing a battery to go flat, then jump-starting it from a car or van, which often finishes it off, effectively ‘frying it’. And that’s especially true for lithium batteries (see below).
If you live where winter temperatures drop below freezing, don’t forget that the electrolyte in a totally discharged lead-acid battery is mostly water, and when water freezes it expands by up to 120%, which can crack the battery’s casing and the plates within.
Over-charging, either because the bike has a faulty regulator/rectifier or because the owner is using an inappropriate charger, is next on the list; when overcharged, lead-acid batteries generate excessive hydrogen and oxygen that will escape the battery, depleting the electrolyte.
If you have a multimeter, it’s easy to test a bike battery, but there is a simpler way…
Multimeters can look a bit intimidating, with a dial covered in unfamiliar symbols, but testing your bike’s voltage is simple.
With the ignition OFF, set the multimeter to the 20V DC (direct current) range, then connect it to the positive and negative terminals of the battery.
A healthy 12V battery should give a reading between 12.5V and 12.9V (a wet cell should be 12.4V to 12.6V, while an AGM should be 12.7V to 12.9V).
Ideally test a battery around 12 hours after the bike has been parked; immediately following riding the voltage will be higher than normal, but once it cools down it drops to its true state of charge.
Next, start the engine and rev to between 3,000–4,000 rpm. This will indicate the voltage being put out by the alternator; an ideal charging range is between 14V to 14.5V, but down to 13.5V is acceptable.
Some modern motorcycles have two-stage charging systems and could reduce the charging voltage below 14V once it has returned the power used during cranking of the engine. A higher charge level is typically seen on older bikes / systems, with up to 15V considered the absolute maximum acceptable level. Anything over that and your battery will be in trouble quickly.
Check your owner’s manual for the exact upper value as anything above that and the voltage regulator is faulty, which will cause the battery to overheat and fail.
Too low, and the alternator is not generating sufficient current to recharge the battery on the move.
If that sounds too technical, OptiMate makes a plug-and-play tester – the TS120 – which uses simple icons to indicate that everything is OK, or to highlight potential problems. This can save you some grief and money, particularly when buying a used bike.
Car batteries are physically much bigger than motorcycle batteries, so they need a more powerful charger. At the most basic level, it would take days to recharge a car with a motorcycle charger, but a car charger could potentially overwhelm a bike battery and cause it to overheat and fail.
Chargers that have the power to cope with car batteries, but that are also safe for use on bikes are available, like the OptiMate 6 Ampmatic, which automatically regulates charge according to the connected battery’s size.
A simple trickle charger drip-feeds current into a battery until it’s ‘full’, then shuts off and waits for the battery voltage to drop below a set level before it will reset and turn back on.
There are two problems with this; firstly, those types of chargers might not deliver a high enough initial charge, so never get the battery to full capacity.
Secondly, a basic trickle charger won’t maintain a battery and effectively protect it against self-discharge – once it decides the battery is charged, that’s it until the battery is discharged and it turns back on.
More advanced chargers are a much better option for making sure your bike’s ready to go and getting the best life out of a battery. OptiMate devices, for instance, not only adjust the charging current to suit the battery, they also have a unique cycle; during every hour of maintenance they charge for 30 minutes at a safe float voltage, then rest and monitor the battery for the alternate half an hour, checking to see if it’s losing charge. That way, if the battery has lost a little charge, it will be topped up again automatically.
Remember, no lead-sulphate, no problem!
I’ve had this charger for about 20 years and used it on at least as many bikes
The problem is that the motorcycle manufacturer doesn’t know what charger you’ll be using. If it’s too powerful for a small motorcycle battery, overheating can be a problem and it could even cause a power spike; companies have to be covered for any eventuality, so if a battery were to explode, or the electronics get damaged, they need to be able to say that they warned you.
Did you know... OptiMate makes chargers for many bike manufacturers to sell under their own brand so that owners can safely charge and maintain the battery – and stay in warranty – without needing to remove it.
Charging batteries in CANbus systems is no more risky than traditional hard-wired types. However, particularly with BMW, when the ignition is turned off the CANbus can isolate the battery. The OptiMate 4 CANbus edition has a digital ‘key’ that activates the system and maintains the battery so you can plug the charger into a DIN power socket and maintain the battery without lifting the seat or installing a fly-lead.
Lithium-Ion batteries pack a powerful punch, so you can start an engine with a battery that’s much smaller – and lighter – than traditional lead-acid. Saving weight and space is a big deal for bike designers, but there are downsides to the tech, not least the increased price…
Yes, of course, providing they’re treated properly.
If you overcharge a lithium battery it can catch fire, so if you’re thinking of changing from lead-acid it’s essential to check that your bike’s charging system is suitable; if the charging voltage is over 14.6V, forget it as that's the safe upper limit for a lithium motorcycle battery. The worst thing for a lithium battery is being overcharged; you don’t want to do that. Ever!
A lithium battery has a much slower self-discharge rate than a lead-acid battery, but most modern bikes draw some power even when parked up (and especially if they have an alarm or tracker); lithium cells must not be discharged too far or they’ll be permanently damaged, so you’ll also need to buy a charger that’s designed for lithium packs.
There is a lot of confusion with this as the term ‘lithium-ion’ refers to the technology rather than a battery’s chemistry. To further confuse things, different lithium battery chemistries have different cell voltages, but that's your best clue as to which lithium-ion technology is in use on the vehicle or within a device.
There are two ‘main’ nominal cell voltages: 3.2V-3.3V and 3.6V-3.7V.
A motorcycle battery made with Lithium Ferrous Phosphate (LiFePO4) technology – also known as Lithium Iron Phosphate or Lithium Nano Phosphate – has four 3.2V cells in series that add up to 12.8V and can be charged to 14.4V (or maximum 14.6V).
Some manufacturers may state 3.3V per cell purely for marketing purposes, and then claim to have a 13.2V battery, but while some bike battery acronyms that have become popular are LFP or LiFe, if it’s a motorcycle starter battery, it’s a 12.8V LiFePO4.
There are other Lithium-Ion chemistries like Lithium Cobalt Oxide (LiCo), Lithium Manganese (LiMN) or even a combination of the two, which is sometimes also known as Lithium Polymer – mainly due to the cell being a soft pack – but all of these have cell voltages of 3.6-3.7V.
The only device used in motorcycles that has this technology is a lithium jump starter pack, made up of three 3.7V cells in series, making it an 11.1V battery that can be charged up to 12.6V maximum. That’s why those jump starter packs have a big diode in line with the red battery clip on the provided set of clamps – to prevent voltage pushing back into the pack when the engine has started up.
No lithium-Ion technologies can deal with overcharge and all will eventually heat up to a point where they self-combust.
Other devices with 3.7V cells (or multiples thereof) are mobile phones, GPS units, cameras… basically anything portable with a lithium battery has 3.7V technology.
A lithium battery is significantly lighter than lead-acid
Inside each cell is an anode made of carbon, a cathode made of lithium ferrous phosphate and an electrolyte that contains lithium perchloride. When totally discharged, all the lithium is in the cathode and electrolyte, but as the battery is charged, the lithium ions move to the carbon anode.
Carbon is porous, so those lithium ions fill the holes and the battery is sufficiently charged when all the holes have been filled.
When you discharge the battery, the lithium ions move the other way, from anode to cathode. As they move through the electrolyte, they cause the electrical ions in the battery and connected circuitry to vibrate, and you have power.
Simple, right? Well, with some caveats. When discharging, you don’t want to completely empty the carbon anode and when charging, you don’t want to stuff that anode with more than it can take, nor do you want to move all the lithium ions away from the cathode.
During over-discharge, when the carbon anode is starved of atoms (i.e. if all the atoms have congregated at the cathode), it starts breaking up as the gaps/holes left by the vacating atoms crumble.
During overcharging, two things happen; at the cathode the holes left by the departing atoms seal up and at the anode too many atoms are trying to get in, so they start hitting against the anode and heat up. We all know what happens when carbon overheats – it starts burning.
Unlike lead-acid batteries, it’s a good long-term strategy NOT to fully charge the battery, but don’t let it discharge too much, ideally not below 30%, or about 13V.
Lithium batteries have real advantages, but you need a good reason to fit one. They generally offer plenty of cold cranking amps and are light-weight, ideal for more aggressive riding on and off road and where a minimum of electrical devices need power when the bike’s not running.
BUT, if your bike runs lots of high-tech electronics or a tracker, the battery will run out of power pretty quickly.
For long distance touring and if weight and space aren’t critically important, you might as well stick with a good quality AGM lead-acid battery. On top of that, if your motorcycle charging system operates at over 14.6 volts, it’ll fry a lithium battery.
You MUST use a specialist lithium charger. These aren’t necessarily expensive – the entry level OptiMate 1 Duo will charge both lead-acid and lithium batteries – but subject a lithium battery to a voltage that’s too high and you could permanently damage it or even cause a fire.
But it’s when you forget to charge it that it can become a problem too.
Lithium batteries are in a sensitive and vulnerable state when their voltage is below 12V, and that becomes critical below 8V, when the battery needs low current until it’s healthy enough to accept a normal charge. Regular chargers designed for lead-acid batteries deliver high current at low voltage and then taper off, whereas a specialist lithium battery charger delivers a controlled low current charge until it reaches 12.8V.
Also, some lithium batteries have a built-in protection system called a BMS (battery management system) that shuts off power to the battery posts if the voltage has dropped too low (usually below 8-9V). To reset the BMS and recharge that battery you need a specialist lithium charger like the OptiMate Lithium 4s 0.8A, which can even save that battery from as low as 0.5V.
If you’ve spent the money on the latest battery technology, don’t forget about the matching charger. Think of it this way; if you owned a Ducati Panigale, would you fill it with low-grade fuel or use the cheapest tyres?