On paper, AGM batteries appear to

be the best for motorcycles because of their low self-discharge rates, hearty construction, low susceptibility to sulfation, ability to function in low ambient temperatures, and resistance to damage and failure when deep cycled. AGM batteries require a pur- pose-built charger, however, as they are easily damaged by improper charging practices. I’ve been using an OptiMate charger for a number of years with excellent results, as all my motorcycles have AGM batteries in them. The reason many people confuse

gel and AGM batteries is because they are similar in many of their character- istics. Their chemical processes are identical, in that oxygen produced by the positive plate is absorbed into the negative plate, which subsequently produces water (instead of hydrogen); this is why we don’t have to top them up like a wet lead-acid battery. Lithium-iron batteries are a varia-

tion on the lithium-ion batteries used to power consumer electronics like laptop computers and smartphones. Their chemical notation, LiFePO4, means that for every atom of lithium (Li) present, there is one atom each of iron (Fe) and phosphorus (P) as well as four atoms of oxygen (O4). When phosphorus and oxygen exist together in a 1:3 or 1:4 ratio in the same mole- cule, that molecule is called a phos- phate. A lithium-iron battery contains inorganic phosphates, while organic phosphates are used in herbicides, insecticides and nerve agents. Organic phosphates are toxic to most insects and animals,


humans. For the remainder of this article, we’ll refer to lithium-iron bat- teries as LFP, which stands for lithium ferrous phosphate, the easy-to-say version of LiFePO4. LFPs are currently the safest, most

fire-resistant and most powerful form of rechargeable lithium-based battery, but because the technology is new,

40 BMW OWNERS NEWS October 2017

they are difficult and expensive to manufac- ture. The biggest benefit of the LFP battery is that its discharge rate remains consistent almost until it is completely discharged, providing a steady, reliable source of power. The disadvantage of this is that you get almost no indication that the battery has reached the end of its functional service life. One day it works perfectly, the next day it’s worthless. When it comes to myths and LFP batter-

ies, there are many going around, so let’s take a look at them and see if we can get into the differences between AGM and LFP.

Myth: Lithium batteries are lighter

than AGM batteries. This isn’t a myth, it’s true. Lithium batteries tend to be smaller in size and lighter in weight than AGM batteries used for the same application. A typical AGM battery for a BMW motorcycle weighs about 15 pounds, while a lithium battery for the same application weighs just under five pounds. While this may be attractive for a race bike, where every ounce is critical, an R 1200 GS weighs 580 pounds with an empty gas tank! Saving ten pounds on a 600- pound motorcycle should probably not be the primary consideration for choosing a battery.

Myth: LFP and AGM batteries are

the same. If this were true, we’d call them the same thing. They’re quite different, and in fact, not understanding these differences can result in a damaged battery. A fully charged AGM battery will show a voltage of about 12.8 volts. An LFP battery that reads 12.8 volts, measured across the terminals and with no load on the battery, is down at least a full volt from its fully charged state. This is why a lithium battery reading at 12 or 12.1 volts will have trouble starting the motor- cycle.

Myth: An LFP battery won’t start

my bike if it’s cold outside. A clear disadvantage of LFP batteries is that they often have difficulty starting a motor- cycle in cold weather. One way to get

around this problem is to turn the ignition on, wait for 30 seconds or a minute, and then try to start the motorcycle. It may take a few attempts to start the bike with a LFP battery when the weather is cold, so patience is often rewarded. A better solu- tion is to combine the above with keeping your LFP battery on a proper charger.

Myth: An LFP battery has a higher

capacity than an AGM battery. A standard AGM battery will have six cells of about two volts each, while a standard LFP battery has four cells of about three volts each. In other words, both are 12-volt batteries. However, when you look at bat- tery capacity, the number to look at is called “amp-hours” (Ah), which lithium battery manufacturers derive from a “lead equiva- lency” (PbEq) rating. A battery with a PbEq of 20 may only have six amp-hours of capacity, which is actually less than an AGM battery—up to four times less! What happens as a result is that a rider may charge their GPS, comm system, Go Pro camera, cell phone, etc. and end up surprised that their LFP battery is dead after just one or two days.

The solution to this is to check out the

true amp-hour rate that some LFP battery manufacturers are starting to list on their packages. A standard Odyssey AGM bat- tery for a bike like a K 1600 GTL has 16 amp-hours of capacity, so compare an LFP battery to that.

Myth: It’s impossible to overcharge

a lithium battery. Maximum voltage for an LFP battery is 14.6 volts. Higher voltages will damage the cells, degrading their ability to be recharged. More importantly, damaged cells in a lith- ium battery may overheat when recharged, which could not only damage the other cells in the battery, but could, in rare cases, start a fire and do far more damage.

Myth: Lithium batteries must be

kept fully charged at all times. LFP batteries tend to function best when kept between 13.05 and 13.6 volts, but if they are discharged below 10 volts, that

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