Lithium electric bicycle battery

36V 10AH Li-ion E-bike battey

LiFePO4 battery for electric bicycles


These electric bicycle batteries are available for sale


At present there are two types of battery commonly used…
Sealed lead acid batteries and various compounds with lithium.
Its weight versus cost. About 3 times as heavy versus 3 times as expensive.
While the cost of lead acid batteries is largely determined by the cost of industrial lead and sulphuric acid, the cost of the lithium ion batteries is largely determined by the technology rather than the cost of the lithium compounds, and is likely to become less with volume production. The sealed lead acid batteries are made with 2, 3 or 4 small 12 volt batteries connected in series within a case. “Sealed” means just that…no vent, no need for topping up, no need to be kept upright.
The lithium batteries are like a bigger laptop battery. They are made with a stack of many 3.7 volt cells in series. There has been, and continues to be an evolution of various lithium compounds, co-compounds, and compositions aimed at better performance, delivery and “life”.
The lithium batteries used in electric bicycles are generally referred to as being “lithium-ion”.
The “lithium-ion” is the cathode of the battery. There has been an evolution of lithium-ion formulations.
The most commonly used is Lithium Manganese Oxide (LiMnO2).
A better cathode formulation than the common LiMnO2 is Lithium Iron Phosphate (LiFePO4, or LFP).
A battery with LiFePO4 can have twice the life, (up to 2000 charges) and is much more stable and safer in use, and being transported. These are likely to be the batteries powering e-cars, e-trucks, e-buses, and e-bikes too. They cost a little more (about %20) but the extra cost is worth it for the extra “life”.
Why aren’t LiFePO4 batteries used more? Probably because they cost about 20% more, and the factories in China are reluctant to switch an assembly line that is producing thousands of li-ion batteries to make a smaller number of LFP batteries.
A technology for the near future might be capacitance batteries…A giant capacitor about the same size and weight as a lithium battery and also holding about the same energy but, at present costing much more, whose advantage is very rapid charging.

There is no predetermined “life” as such.
It’s just that by the time the battery only has 60% of its original capacity it is losing capacity, and usefulness, quickly and for most purposes needs to be replaced soon, and so that’s it’s “life”.
The battery factories test their batteries with a series of charge/discharge cycles.
Of course they don’t get on a bike and ride it for 2 hours each time, but instead discharge in the laboratory through a resistive load. They produce a capacity versus discharges chart and a certificate saying 300, 800 or 2000 etc discharges reduce the battery’s energy to 80% of original.
In practice, on the streets, however, a battery will not do so well.
There are many factors that affect how long a battery will give a useful service.
To start with all batteries will deteriorate by a small % every month, however they are used, and even if not used.
I suspect some of the many factories in China use inferior BMS cards and electrolyte, and do not test sufficiently.

Other factors affecting the battery’s life include :

  • Rough treatment.
  • Being kept or left in a hot place (or being left in the sun). This is a big effect. Please park your bike in the shade.
  • Partial discharge/recharges should give proportionally more recharges.
  • Being left unrecharged for more than a few months, particularly if it was flat at the time it was left)…(however they should also not be left for a long time fully charged either- about half charged is better)
  • Battery type – LiFePO4 batteries fade with time much less than do common “li-ion” batteries.
  • Quality. Individual cells (it just takes one to fail) or BMS can fail well before battery otherwise loses capacity

More About Lithium Batteries

For the science of, the advantages of, the problems with, the history of, and future of the various types of Lithium-ion” battery I suggest those of you interested in delving further into it refer to :
Li-ion, lithium polymer, or LiFePO4 batteries on Battery University

Taking Care of a Lithium Battery
The lithium battery is the most expensive part of your electric bicycle.
It is very worth while your taking good care of it. It will have its own built in Battery Management System (BMS) that should protect it against its being short circuited, its overheating, or cells within it that don’t do their equal share of taking a charge and giving it back. The BMS is not a 100% guardian.

They should not be overcharged. The charger should power down when the battery is charged, but if the charger indicates “charged” disconnect it anyway. Leaving chargers “on” will reduce their life in any case. The charger should turn off when the current is low. Don’t as a custom leave chargers on all night.
Note also that 36 volt battery chargers are NOT all the same. Do not use one meant for a lead-acid battery to charge a li-ion battery, or LithiumIronPhosphate or vice versa.
LiFePO4 batteries are charged at a slightly higher voltage than Li-ion batteries (43.8v vs 42v) and should have a charger meant for LiFePO4 batteries. A “LiIronPhosphate” charger will overcharge a Li-ion if left charging. A Li-ion charger will undercharge a LFP battery.

With the old style single pin charging socket be careful not to short circuit the socket. Connect charger to battery first.

The batteries will age quicker when fully, or nearly, charged.
The more time they spend fully charged the less will be their life.
If the bike is not going to be used soon then leave charging until soon before you expect to use it.
Also frequent topping up is not recommended for similar reason.
The power from the battery is quite constant until about 70% of the energy is used.
It’s a misconception that a full battery gives more power.
Li-ion batteries do not have a memory effect. You don’t want to risk running the battery flat, but if your use is generally short trips then it is best to go around 2/3 of battery range before recharging.
Temperature extremes have a big effect on life of a battery.
The life reduces more if used above 50degC or below 10degC.
They should not be left in sun, or stored in a hot place.
If it has been in sun or hot place allow it to cool before use.
Parking your bike in a place with full sun every day will be the greatest factor in reducing the life of the battery. The battery ages more slowly if stored in a cool place, even in refrigerator
(not freezer), but then do allow it to warm up before use.
Your battery should not be left unused unrecharged for more than a few months, lest the constant trickle of current used by the battery’s management system take the voltage down to a critical level. (Particularly if it was flat at the time it is left)…However they should also not be left for a long time fully charged either as that too reduces life. About half charged is better.
There is a much misinformation about “li-ion” batteries. To be better informed follow the link above.

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anything you wanted to know about electric bikes