Rechargeable lithium-ion batteries are used in all sorts of common portable devices, including cordless power tools, cell phones, laptops, and tablets. Lithium-ion cells have made nickel-cadmium and nickel-metal hydride batteries outmoded, and lithium-ion batteries are making inroads into the motorcycle market. The safest lithium-ion battery chemistry used for starting engines is lithium ferrous phosphate (LiFePO4), sometimes also known as lithium iron phosphate or LiFe/LFP 4-cell batteries.
There are a number of reasons why they’ve become so popular. LiFe/LFP batteries are light (lithium is the lightest metal known) and have high storage capacity (energy density) for their size. They also have little memory effect (tendency to lose capacity due to improper charging regimens) and their self-discharge rates are low. When stored and not connected to circuitry, they typically lose 1% to 3% of their charge each month. By comparison, lead-acid batteries typically self-discharge at around 5% per month.
The charging systems of most motorcycles produce voltages compatible with LiFe/LFP batteries. A LiFe/LFP cell’s nominal voltage, depending on the electrode materials, is between 3.2 and 3.3 volts. So with four cells in series (for a “12-volt” battery) that’s 12.8 to 13.2 volts, compared with 12 volts (6 x 2 V cells) for a lead-acid battery. You need a charging system/regulator that keeps the voltage between 13.8 and 14.5 volts. If it’s higher than 14.5, you will run into problems, as LiFe/LFP batteries, just like any lithium-ion type of battery, do not tolerate overcharging. Lithium-ion batteries overheat when overcharged. At 15 volts and above you will run into serious problems: The battery will swell, overheat, and could melt down. Tip: Make sure your vehicle’s charging system is working in that zone of 13.8 to 14.5 volts before considering a LiFe/LFP battery.
For storage and deep (low volt) recharging, special chargers are recommended for LiFe/LFP batteries. Unlike lead-acids that should be kept fully charged at all times to avoid the battery losing capacity, LiFe/LFP batteries last longest if kept somewhere between 70% and 90% (13.3 to 13.6 volts) when the motorcycle is stored.
LiFe/LFP batteries work best near room temperature and can be fast-charged within the temperature range of 32 F to 113 F (0 C to 45 C). Charging should be performed within this temperature range. From -4 F to 32 F (-20 C to 0 C), charging current should be reduced. When temperatures get near freezing, the batteries may need to be warmed up before use. This may be done by turning on the lights for a couple minutes until the battery “wakes up.”
Certain lithium-ion batteries have been known to catch fire when used or charged improperly, but the LiFe/LFP (lithium iron phosphate) chemistry used in motorcycle lithium batteries is far more stable, with a higher runaway temperature of 518 F / 270 C, almost 1 ½ times higher than what’s used in a smartphone. (Runaway temperature is that critical temperature when it will start to self-consume, heat itself, and catch fire). However, a lithium-ion battery’s temperature increases during use and during normal charging. Tip: If you’ve been riding all day in hot weather, only hook up the maintenance charger once your bike has cooled. By that time the LiFe/LFP battery would have cooled as well.