Depleting Lithium Batteries

[Bernie9927]

Hi you good people. I have a 24 volt Lithium-ion E-Bike and one of the conditions on battery maintenance is that if left for a longish period, I should ensure the battery is left at about 40% or thereabouts. However, I recently charged the battery to 100% with the intention of riding it the next day but due to sudden medical reasons, I was unable to do so and the bike was left in this state of charge for longer than normal. Although no harm was done in this instance, it made me think how I would be able to deplete the battery's charge should it happen again, especially for several months.

My first thought was to connect a 24 volt 21w auto bulb via the battery's power outlet but I do not wish to do this, as there are four concealed connections and I am just not sure which are the correct ones to attach to. However, as I can get a voltage reading from my multimeter when I attach it to the charging point via an Alumberg plug, could I deplete the battery this way ? This must be a common problem with battery powered bikes and I would very much appreciate some advice, please.

Bernie

[Marcus Aurelius]

A state of 100 percent is fine for a lithion cell. What’s being said is that you shouldn’t let it go below 40 percent before recharging to maximise it’s life. The worst that can happen is that it’s life is shortened ( but not by much ) if you don’t. Warranty companies won’t quibble unless you’ve continually gone from 100 % to 0% and killed it that way.

[hemo]

100% will lessen the battery life, you won't see voltage lessen but over time capacity will. Loss of capacity is a loss of range as well as a sign of cells aging, aging cells suffer in use with voltage sag or in extreme cases voltage collapse when a load is applied.
Using 12v/24v bulbs isn't an issue so connect them up and discharge to between 3.6 - 3.85v per cell group.

[stodd]

just to clarify, that is per cell, so from just over 25v to just under 27v for the battery.

[hemo]

just to clarify, that is per cell, so from just over 25v to just under 27v for the battery.

Quite right Stodd, I have edited my post to say this and should have mentioned it when I originally posted.

[Bernie9927]

Many thanks for your replies.

Hemo got nearest to answering my query but but did not go so far as to say that I could safely use use the charging point. Can I do so Hemo?

As a matter of interest, my battery's manual clearly states that if I had to store it for a long period, say 3 months, then I should do so at around 40% charge and I think this is common knowledge with Lithium batteries. However, it does not tell you how you can safely reduce the charge and being a Vietnamese Company, I don't think I would get any sense out of them if I emailed!!!

Bernie

[hemo]

Bernie no you can't discharge via the charge port as the BMS inside uses two separate channels for the control of both charge/discharge. Same port BMS are available for the diyer but they are not used generically in batteries.
The use of 12v bulbs in series or a 24v bulb is common place, a bike with throttle can be left in a stand with throttle tied open to reduce voltage or ask a friend to ride the bike around the block for you.

Most battery cells are shipped by manufacturers/suppliers at approx. 3.5v - 3.7v per cell, no harm is done if cells are left at up to 3.85v per cell. For a 24v /7s battery 3.5v per cell is 24.5v Soc or 3.85v per cell is 26.95 Soc. Soc = State of charge.

The advantage of leaving a battery equal to 3.85v per cell is if it isn't checked for several moths the higher voltage allows for any self discharge should it occur, if leaving a battery at 40% or about 3.5v per cell then it is advisable just to check them once a month to ensure self discharge doesn't cause the BMS to shut down because of low cell imbalance. If a cell group self discharges to low typically <3.2v per cell then the BMS will shut down and disable the charge function, the battery then needs opening and manual manipulation is required to charge any low cell groups up to then allow the BMS to work again.

[Bernie9927]

Thanks Hemo. I had a feeling the charge point would be out of the question, so I am glad I asked beforehand. I will just ensure the situation I outlined never happens. Unfortunately, my bike is "Battery Assist" with no throttle, so I will forget the whole idea as I don't like the idea of someone else riding my new bike !!

Regards

Bernie

[billym444]

as said fully charging your battery and leaving it stood now and then isnt going to do it major harm. but constantly topping it up to full to let it stand, wont do it any good. will shorten its life.

i have a luna smart and it has 80% for standing 90% for everyday use and 100% if you planing heavy use.

as also been said it more dangerous to stand to far discharged. i wouldn't let it satnd for long under 22 or 23v i would look at 24 to 25v for long term standing, quick check once a month.