KNOWLEDGE
Buying batteries used to be simple, even if maintenance wasn’t. But now, with multiple options available, things have got complicated. This is what you need to know
Illustration GS YUASA CORPORATION
Bob Dixon
‘I’ve used lithium batteries in race bikes, but to be honest I wouldn't bother for the road. Although I do much prefer AGM to old-style high-maintenance lead acid.’
What are the options?
LEAD ACID (LA)
Also known as a flooded or wet cell battery. This is the conventional old-style battery in which lead plates (positive and negative) are built into a case, each separated by a rubber barrier and the plates submerged in electrolyte. The sale of the acid packs which used to be supplied with these types of batteries is now banned. If you want a lead/acid battery, you should be collecting it filled and charged, from the shop.
Pros Cheap. Wide operating temperature range from below freezing to 100°F-plus. Relatively low self discharge rate.
Cons Needs regular topping up, risk of spills means they must be mounted vertically. Discharging by over 50% can damage the battery.
SEALED LEAD ACID (SLA)
Sometimes referred to as VRLA (Valve Regulated Lead Acid). Similar construction to old-style LA battery, but electrolyte is sealed into the battery and the gases created during the charging process are controlled by the valve system. Increasingly superseded by AGM batteries.
Pros Same as for the LA above, plus maintenance-free. Can be mounted in any orientation (except upside-down).
Cons Discharging by over 50% can damage the battery.
GEL BATTERY
A lead-based battery with acid in gel form instead of a liquid. Specified as OE on some bikes, but have now been more or less superseded by the AGM type.
Pros More tolerant to deeper discharge rates than a standard LA or SLA.
Cons Sensitive to excessive charging voltages (over 14.4v). Size for size, will store less power than an AGM and cold weather performance not as effective.
ABSORBENT GLASS MAT (AGM) AGM batteries are constructed with a layer of glass mat sandwiched between the cells. This layer holds the electrolyte in place so the plates are permanently immersed, making the battery more efficient. Now effectively the standard replacement battery for motorcycle use.
Pros All the advantages of SLA, plus they are less prone to sulfation (see right) and can be stored for longer periods without needing to be charged. Vibration resistance makes them ideal for motorcycle use.AGMs also accept a faster charge rate than a than a conventional SLA battery and are more tolerant to deep discharge.
Cons Higher cost than basic LA types.
LITHIUM (LIFEP04)
Lithium battery cells have a nominal voltage of 3.2v and four are arranged in series to create a 12.8v battery.
Pros High energy to weight ratio (up to four times greater than an LA) which means lithium batteries are much lighter than equivalent lead acid batteries. More starting power than a lead acid. No leakage. Fast charging capability.
Cons High cost. Lithium batteries are intolerant of over and undercharging, either of which causes damage. Also less tolerant of cold than a conventional LA. They absorb heat faster than other types, which can lead to premature failure if sited in a hot environment. Lithium batteries need an inbuilt battery management system (BMS) to protect each cell from excessive voltage during charging, overheating and over current during discharging. In worst case scenarios, lithium batteries can explode or catch fire if the charger isn’t properly regulated. Confirm any lithium battery has aBMS and only buy from reputable suppliers.
What’s inside?
Absorbent Glass Mat battery features electrolyteimpregnated mat beween the lead plates, and a safety valve to release any excess pressure. There’s no need for a translucent case, because there is no need to check the level of acid in the battery.
What do the numbers mean?
There are two commonly used methods of rating a battery’s output; the amp-hour (Ah) rating quantifies the amount of power a battery can be expected to deliver over a specified time, operating in a temperature of 25°C. Abattery rated at 10Ah should deliver one amp for 10 hours (or two amps for five hours) without recharging.
The other method of rating output is to quote the cold cranking amps (CCA). This tells you how much current a fully charged 12v battery will deliver for 30 seconds at -18°C, while maintaining voltage above a specified threshold. A high quality 10Ah battery might have a CCA rating of 180amps. CCA ratings are particularly relevant for electric start bikes with high compression/large capacity.
Battery code numbers such as YTX12BS or YB7-A mainly relate to the battery’s dimensions. Ideally, use the battery code specified by the bike’s manufacturer unless your battery supplier will guarantee that an alternative code will fit.
How can I extend battery life?
Battery life is dictated by sulfation and ‘shedding’. Shedding is the unavoidable result of the plates expanding and contracting during the charging and discharging process, shedding small particles off the plates. A decent quality battery will have a life expectancy of approximately 500 charge/discharge cycles, ie typically 500 days of use.
Sulfation is the process in which small crystals of sulfate in electrolyte attach themselves to the plates. In normal cycles of use, the crystals detach themselves (smart chargers recreate these conditions to prolong battery life). But if the battery is left discharged, the crystals can permanently attach to the plates, acting as a barrier, preventing electrolyte from saturating the plates and thereby making the battery less efficient.
A completely discharged battery is unlikely to recover, so disconnect the battery if the bike is parked for over two weeks. Ideally, a battery should have 12.7-12.8v when stored and, to prevent condensation leading to internal corrosion, shouldn’t be stored in the cold, and especially not on a concrete floor. If you don’t want to leave the battery in situ on the bike, store it somehwere dry, well ventilated and away from draughts.
If, after a couple of months, the voltage drops to 12.5v or less, recharge it; 12.4v is approximately 60% charged, normal on a vehicle too low for long-term storage.