There are a host of myths about Lithium batteries, many more than there used to be about lead acid. One reason is the various chemistries lumped under a single name, but also there are the somewhat strange ways that they work, age, degrade, and get damaged. We’re not going to dive deep into the chemistries other than the few places it makes sense to. Instead we’re going to look at them in specific applications and show you how and where they work well.
This first application is as the main battery in a motorcycle. This is a fairly new application. Lithium motorcycle batteries reached the aftermarket around 2008–2010. Before 2008 the batteries were racing only, mostly in MotoGP and Superbike racing where a pound saved is a big deal. Ballistic Performance started selling a few formats for street use in 2008 and Antigravity sold racing batteries. About 2010 Shorai launched it’s LiFePO4 batteries (generally shortened to LiFe) and by 2011 to 2013 AntiGravity, EarthX and Skyrich had fairly complete street ranges covering most popular formats either directly or functionally duplicating AGM formats. Some motorcycle manufacturers started using them in premium models in 2010, with more manufacturers adopting them by 2020. Even the earliest batteries were generally LiFe not the lithium cobalt or NMC cells because LiFe is much less prone to catching fire, and its 4-cell voltage of about 13.2 V matches charging and operating voltages of what we call a 12V system (which is almost never 12 volt).
Myth 1: Lithium batteries are dangerous in a motorcycle and will get overcharged (or undercharged) which makes them catch fire. Reality: A good-quality LiFe battery with a proper BMS is demonstrably as safe as AGM in practice, and safer than flooded lead-acid for everyday handling. A cheap LiFe without protection is the riskiest of the three, and the risk is still low. I’m going to leave that as an unsupported statement for readability and provide sources at the end of this document.
Myth 2: A motorcycle charging system can’t charge lithium batteries. Check the table below and see if you see a problem.
Charge voltages for a 12 V battery
Absorption LA/AGM–14.2–14.6 V 4cell LiFe–14.4 V-14.6 V
Float LA13.2–13.5 V AGM 13.5–13.8 V LiFe None preferred 13.5–13.6 V is OK
Temperature issues: LiFe: Don’t charge below 0 °C.
Resting voltage when full LA12.6–12.7 V AGM12.8–12.9 V LiFe13.3–13.4 V
In actuality, there is a problem with directly charging Lithium batteries. Older motorcycle charging systems, while they are in theory regulated for proper charging voltage, often have a lot of ripple–the voltage delivered from the charging system is not a smooth DC voltage but instead has peaks and valleys substantially above and below the proper DC voltage. This can damage lithium batteries while lead acid or AGM will tolerate ripple well and mitigate it. Lithium batteries tolerate a small amount of ripple, but old mechanical regulators or failing electronic regulators or diodes that wouldn’t do much to LA or AGM batteries can shorten the life of lithium batteries. The easiest way to see if you have a substantial amount of ripple is to set a multimeter to AC and read the voltage across the battery at 4-5,000 RPM. .1 to .3V is fine. .3 to .5V is acceptable, but check occasionally to see if it’s getting worse–it might be an indication of a failing rectifier. From .5V to 1 V indicates a failing rectifier or regulator that will shorten the life of a LiFe battery. More than 1V means your regulator or diode board is toast and will kill your LiFe battery quickly. Check DC volts at the same speed; it should be about 13.8–14.6 V.
With a healthy regulator, ripple isn’t a real concern for LiFePO4. If you’re putting lithium in an older bike, test for ripple first. A MOSFET-type regulator/rectifier is a worthwhile upgrade; it runs cooler and gives cleaner output than the older shunt types. Airhead BMWs with excited field rotors and funky mechanical regulators have astonishing ripple even when they are operating properly. If you want to go to Lithium battery you should consider at least an electronic regulator and really a more modern alternator like an EME enduralast. It’s a good upgrade even if you stick with the massive LA battery common in Airheads. People called Lucas the prince of darkness, in airheads, Bosch is at least the Duke of Darkness.
Myth #3: Lithium batteries can’t crank a motor over more than a few tries. Actually in most cases a Lithium battery cranks a motor faster than a LA or AGM, simply because it’s voltage is higher (generally 13.3V vs 12.9) and the voltage doesn’t drop as quickly as LA batteries. But you do need to choose the right battery. Lithium battery voltage is nearly flat over a wide range of charge, which both complicates the job of the BMS and makes starting feasible over a much wider range of charge than lead-acid batteries.
Size Real capacity (Ah) “PbEq” Ah CCA
LFX09 ~3 9 ~135
LFX14 ~4.6 14 ~210
LFX18 ~6 18 ~270
LFX21 ~7 21 ~315
LFX36 ~12 36 ~540
So what does all this mean? PbEq” or “lead-equivalent” Ah is a bullshit marketing number with a little reality behind it. A lithium battery sold as a “14 Ah equivalent” really holds about 4–5 Ah. CCA is a real number and usually matches or beats the lead-acid battery it replaces.The little bit of reality behind PbEq is usable capacity –You can’t drain lead-acid below 50% without damaging it, and its capacity drops quickly under heavy load. LiFe delivers about 80–90% of its rating at a steady voltage with no damage. So a 4.6 Ah LFP battery behaves more like a 7–9 Ah lead-acid in practice, but still not the bullshit 12Ah PbEq number. I think PbEq is the primary source of disappointment in LiFe batteries. If you size by that number you have little reserve capacity. It still cranks hard when fully charged, but if you leave the lights on, the bike sits for weeks with parasitic loads, or you run heated gear or accessories while idling it might fail to start. And LiFe struggles in the cold. Below about 0 °C (32 °F) it delivers noticeably less until it warms up. A little current draw–like running the lights, will warm the battery quickly. Some folks disparage the weight savings, but LiFe at real capacity parity is much lighter, typically 60–75% less weight. For a 14-size battery that’s about 1–1.5 kg instead of about 4 kg. Given the high mounting of batteries in most bikes, that affects handling and your ability to pick the bike up after a fall.
So how do you choose a size? if you switch to LiFePO4, ignore PbEq, match or beat the original battery’s CCA, and if you have heavy electrical loads go one size up in real Ah. So if the recommended LA battery has 200 CCA but you use heated clothing bump up to LFX18.
There’s a big difference between LiFe batteries in 2015 and today, and it’s mostly in the BMSs which are more sophisticated and add reliable starting features. Many people say something like “I had one (or my buddy had one) and he always had trouble cold starting”. Welcome to the 2020’s I recently switched my hard-starting 701E to Lithium by simply switching in a LiFe battery after checking for ripple (about .2V at 4000 rpm). It starts much better, powers my heated jacket happily, and I dropped three pounds as a minor side benefit.
Here’s a bonus tip–most manufacturers say not to jump start LiFe batteries. That’s because they don’t trust you to do it right. Here’s the cautions that matter more than an LA battery jump start: A small lithium jump pack or another bike is the best source. Both match the battery’s needs well. If you use a car, keep its engine off. A running alternator pushed system boltage to 14+ volts. That plus a large lead-acid battery can push a big surge of current into a flat lithium battery. That can exceed its charge rating . That’s really what the manufacturers are worried about.
If the battery is totally dead–meaning you read 0V across the terminals, the BMS has probably disconnected the battery to protect it from deep discharge. Jumping may not work. Some batteries have a wake-up or reset button, and Antigravity’s RE-START models keep a hidden reserve you unlock with a button or fob. Otherwise you need a lithium charger with a wake-up mode.
After a jump, it’s best to charge the battery with a lithium charger instead of relying on riding–but of course that isn’t always possible. But take it easy for a while–rpm under 3500 for most bikes. Refilling a very flat battery works the stator and regulator hard. If it sat below about 8 V (2 V per cell) for a long time, the cells may be damaged. Charge it, then load-test it before you trust it again. Using your LiFe bike battery to jump another bike is usually OK. Don’t try to jump a car with it; it’s too small and the BMS will likely cut out. It’s a different chemistry and electronics than the magic little “Lithium” (generally NMC chemistry) jump packs.
I know all this sounds like a PITA, it’s not. LiFe batteries are just different, and in general they are much better. They last longer, start better, and are more reliable. They used to cost a lot more, now they don’t. In reality you put them into your bike and ignore them. If you store your bike it’s worthwhile disconnecting the negative lead to insure you don’t have parasitic loads, and then you don’t need a battery tender to float it–over a 6 month period they generally lose 5-10% charge vs. an LA battery going dead or losing a cell.