Monday 6 January 2020

Lithium Motorcycle Batteries

LifePo4 batteries.
Not that long ago if your motorcycle needed a new battery you simply had to decide between various types of lead acid batteries. They all use the same chemistry and only differed in terms of how that chemistry is packaged and the quality of build.

Wet fill lead acids batteries are always the lowest cost, and to be honest in a kick start bike with no high current loads they last OK. They often die simply due to lack of maintenance as the acid level slowly drops over time and needs topping up with distilled water.

Absorbent Glass Matt or AGM offer more convenience and are often sold as zero maintenance. They are filled with a pre-measured amount of battery acid either by the shop or the owner just before fitting, the top is then sealed and that’s that, no further maintenance can be done. The chemistry is just the same as wet fill, but the acid is held in a fibre glass matt and this matt can be very thin so AGM batteries can be built with the plates closer together and in some cases with more plates per cell, this in turn allows them to supply higher current which is useful for electric start bike.

Top end specialist sealed batteries, these were always factory filled and supplied pretty much ready to fit. They are variations on the AGM battery, but built to a very high quality, some even have spiral plates to increase the surface area. These are always the most expensive lead acid type, but often offer much higher maximum current known as Cold Cranking Amps (CCA) which can be very useful for higher compression electric start bikes or those used in the winter.

But now there is a range of lithium batteries designed to directly replace the lead acid battery in your motorcycle.
It’s important to understand the terminology as “Lithium Technology” seems to cover a range of different types of battery. All are often referred to as Li-ion or Lithium Ion.

Lithium-Cobalt Oxide or LiCoO2 are the smallish batteries used in mobile phones, they charge slowly, they hold a decent amount of energy for their size and they can be discharged slowly. No use at all for a motorcycle. If LiCoO2 batteries are charged or discharged quickly they can go into thermal runaway and catch fire. There have been famous cases of reputable mobile phone makers demanding too much from these batteries, which lead to some much publicise fires.

Lithium Iron Phosphate or LiFePo4 is the only chemistry currently available (2020) to be trusted in a motorcycle. They store much less energy size for size than either LiCoO2 or lead acid. This sounds like bad news, but it can deliver all of that energy very quickly so it is perfect for electric start bikes. There is no real need to store a lot of energy, as soon as the bike starts the alternator will supply all the energy required. To start a bike the single most important thing is cold cranking amps (CCA).

LiFePo4 safety and maintenance is only a concern if it is not understood. Just like a lead acid battery the LiFePo4 battery is made up of several cells inside a convenient box with a terminal at each end. It is vital that these cells are kept roughly in balance so one does not become deeply discharged while the others are charged. If this happens the battery life will be shortened and there is a very small possibility that during charging, the charger (or regulator on the motorcycle) will not cut out as this one low cell is bringing the total battery voltage down, if this situation continued eventually a fire may start due to overheating. So ONLY consider batteries manufactured with an inbuilt factory fitted Battery Management System know as BMS (sometimes referred to as BMC). This is an internal electrical circuit that monitors the voltage of each cell with in the battery and balances the voltage.

LiFePo4 batteries really do not not like being charged above 15 volts, their life will be dramatically shortened, and given the high cost of LiFePo4 batteries this issue should not be ignored. Before fitting a LiFePo4 battery to any bike it is worth taking a voltage reading across the battery with the engine running at various speeds and with various electrical loads such as light on or off. If the voltage regulator on the bike is doing it’s job it will never peak above 15 volts, or if it does it will be for less than one second as it adjusts to different electrical loads. If using a battery charger it is much better to use a charger designed specifically for LiFePo4 batteries, these will never go above 15 volts but equally they will not supply a very low amp trickle maintenance charge which also shortens the life of LiFePo4 batteries. At a push it is possible to use a standard charger of the correct size, whilst monitoring the voltage with a volt meter. Allow the charger to take the battery to about 14 volts and then turn it off. Earlier I mentioned that LiFePo4 batteries store less energy than AGM batteries, and when it comes to fast charging this is a huge advantage. To charge a discharged bike sized LiFePo4 battery may only take an hour compared to 4 or more hours for a AGM battery.

Lets start comparing AGM with LiFePo4 to understand the difference. All these batteries are exactly the same physical dimension and both fit a Jawa 350 OHC.

Battery type
Full Charge Voltage
Energy stored in AH
Cold Cranking
Lead Acid wet fill
Standard mid range AGM
High end AGM

The table shows some interesting things when it comes to starting an engine. The more amps that are supplied the more torque the starter motor will produce, but also worth noting is the more volts that are supplied the faster the motor will spin.

The total energy stored does need to be considered. If the bike is fitted with any alarm or tracker device with a high drain you will need a lot of storage
however good quality modern alarms should have almost zero drain. Still worth checking if you have an alarm and you are considering a change to a LiFePo4 battery. The alarm manufacturer should be able to tell you the drain on standby, anything below 5 mA should be OK.

If you have read any of our other blogs you will know that at F2 Motorcycles Ltd we like to test stuff before deciding if it’s all hype or a useful product.

As the UK Jawa importer we have two nearly identical bikes available to allow comparative testing. Both are Jawa 350 OHC which are 4 stroke singles with Euro 4 fuel injection and electric start. They use a 9 amp battery mounted behind the side panel and like most modern bikes there is no room for a larger battery. Both bikes have covered less than 2000 miles from new, and both are freshly serviced using the same oils. They are both stored next to each other in an unheated area so the temperature should be the same.

One bike is fitted with mid range new AGM lead acid battery the other fitted with new LiFePo4 battery of same dimensions and sold as direct replacement. After fitting, both batteries were given similar treatment, used to start the bike, allowed to charge, allowed to discharge a little by leaving the lights on, charged, bike started and run for 10 minutes, etc. This treatment continued for a few days and both batteries were always treated in the same way. This was only done as in the past we have experienced brand new AGM batteries not performing well until they have been worked a little. The AGM battery was always charged with a smart charger designed for AGM batteries and the LiFePo4 used a similar size charger but one designed for LiFePo4 batteries.

The batteries were than fully charged using the correct charger and left plugged in until the charger displayed the full charge light. They were then unplugged and left for one hour and the full charge voltage reading taken.

A thermometer that records maximum and minimum temperatures was used to give a range of temperatures during the time between each voltage reading.

The batteries were then monitored over time attached to the bike just as they might be if you left your bike in a cold garage in the winter with no charger.

Voltage after full charge 8.2 °C
Voltage after 24 hours at between 5 and 10 °C
Voltage after 3 days at between 5 and 10 °C
Voltage after 7 days at between 5 and 10 °C
Voltage after 14 days at between 3 and 10 °C
Voltage after 20 days at between 2 and 8 °C
Voltage after 26 days at between 2 and 8 °C
Voltage after 30 days at between 3 and 8 °C

After 30 days an attempt was made to start both bikes.
The temperature was 3.2 °C

AGM results are as you would expect for a battery showing 11.5 volts and a temperature of about 3 °C. The engine turned over very slowly once but the engine did not start. On the second attempt the engine didn’t turn over compression. The battery was rested for 15 minutes to recover and a third attempt made, but again although it managed to take the engine over compression once, it did not start.

LeFePo4 results are much more encouraging. On the first attempt the engine turned over reasonably quickly but failed to start, Waited 10 seconds, and the second attempt turned the engine over even quicker but still failed to start. Waited another 10 seconds and the third attempt spun the engine over very quickly, it started and ran.

Different techniques for different battery technology. Lead acid batteries tend to recover a tiny amount if they are allowed to rest for 15 minutes. LiFePo4 batteries work much better if they are slightly warm and the act of pressing the starter button warms them so by the third attempt with just 10 second rests the battery was performing well. There is advice on line suggesting that on very cold days it is worth turning the lights on or holding the brake on to light up the brake lights for a minute before trying to start the bike.

The first test would seem to show the LiFePo4 as the easy winner, but the AGM battery performance seemed almost too bad to be believed.

The first test seemed too bad to be trusted, experiences says AGM batteries don’t like standing about in the cold, but the results seem terrible. Test repeated using another new battery, but a different make from a different supplier at a higher price. Again it was fitted and used for a few days to cycle it a little before the test started. This time the AGM battery was charged using an intelligent charger with winter mode which holds the peak voltage slightly higher during the float stage of charging. This is cheating slightly as many people will have a smart charger, but not so many will have one with winter mode. However if this proves the AGM battery can be used as a reliable starter in winter, it might be worth knowing. There is no winter mode for LiFePo4 so this was charged using the same charger as the first test.

Lead Acid
Voltage after full charge 9.5 °C
Voltage after 24 hours at between 5 and 10 °C
Voltage after 3 days at between 5 and 10 °C
Voltage after 11 days at between 5 and 12 °C
Voltage after 13 days at between 3 and 12 °C

After just 13 days an attempt was made to start both bikes.
The temperature was 6 °C

Surprisingly AGM even at 12.80 failed to start, First turn seemed hopeful but engine failed to catch, second press engine noticeably slower to turn, Voltage after 15 minutes to recover was 12.50. Further attempts to start fail to produce a running engine and the starter simply got slower with each press. At this point we were getting suspicious that there might be something wrong with the bike rather than the battery, so a second battery was linked in parallel to the bike and it started immediately proving the only thing stopping this bike from starting is the inability of the battery to supply enough power to the starter motor. BUT this second battery is far too big to fit to the bike permanently as it is from a small car.

LiFePo4 battery turned engine over at reasonable speed but did not start on first attempt, waited 15 seconds with the ignition on and brake lever pulled in to activate the brake light. 2nd attempt engine turned quickly and started with no problem.

The problem seems to be modern high compression engines need lots of amps to spin them over, modern electronics need a voltage close to 12 to trigger the injectors and ignition system. Small AGM batteries don’t seem to be able to crank the engine fast while supplying good voltage when they are cold. A much bigger AGM battery would work, but there is no space on a modern bike. The LiFePo4 battery does seem to offer something better than the AGM technology but at a price. There is no getting away from the fact they are much more expensive and in order to last well would need a charger designed for them. The final unknown is battery life. There are reports online of LiFePo4 batteries lasting only a few months, but looking in to these they all seem to be cheap batteries with no BMS fitting or batteries that have been left deeply discharged for a while. Generally a good quality LiFePo4 battery fitted with a well made BMS and kept charged regularly by either riding the bike every couple of weeks or by attaching a LiFePo4 specific charger will out last a mid range AGM but may not last as long as the very best of the best AGM costing as much or more than a LiFePo4.

Based on these results we are now offering LiFePo4 batteries and chargers for the Jawa 350 OHC.

And finally just a recap on the safety and suitability of Lithium Batteries. They may all be marketed as Lithium, Li-ion, Lithium-Ion etc, but the ONLY safe reliable ones are LiFePo4 with high quality BMS designed specifically for vehicle use. If it’s on a dodgy online site and looks to cheap to be true it probably is not a reliable and safe LiFePo4.