How often are you supposed to 'fully charge' your eBike battery?

[LukeJolyon]

I would greatly appreciate some advice form forum members, as I find the advice about caring for the battery on my (lovely) new Orbea Gain F40 totally confusing. It doesn't help I think that it's translated from German, being a Mahle battery.

So it says that I should 'make a full charge at least every 2 months'. My question is, what does a 'full charge' entail?

Elsewhere it says 'A charging process from 0 to 100% is considered a charging cycle. Charging 5 times from 80 to 100% equals a full charge cycle' and also 'charging our battery from 95% to 100%, is a process that besides to a long wait, it could reduce the battery’s overall capacity in its useful life considerably'.

So should I be:

- running it down to 0% and then charging it fully to 100%, once every two months
- just charging it up to 100% instead of 80%, once in every two month period for one of my daily commutes
- charging it 5 times from 80% to 100% - perhaps over the course of one week, every two months

And then how does this fit with the alarming advice that you should NOT charge it from 95% to 100%? I'm pretty sure I've charged it up to 100% once with no problems - should I not have done that? or not be doing it in future?

Any advice very gratefully received!

Thank you all,

Luke

 

[vfr400]

None of that will do anything to lengthen the life of the battery. If you do need to do it, it can only be to calibrate the estimation of range if you have an LCD that predicts range.

The ideal range of use for lithium batteries is between 20% and 80%, but most ebike batteries only balance when they reach 100%, so if you don't charge to 100% full most times, the battery can go out of balance and lose capacity. Without seeing the elctronics in your battery's management system, I can't say that yours works like that, but most batteries do.

In my explanation, charging to 100% means until the green light comes on the charger. maybe that's what they mean too, not all the way from empty to full.

Be aware that over the years, we've seen all sorts of poppycock in ebike manuals regarding the lithium batteries, so I wouldn't take too much notice of it.

 

[LukeJolyon]

Many thanks for that.

I should have explained, I am using the ebikemotion system/app, so it gives me a (presumably) accurate read out of exactly what percentage the battery is at.

So your advice would be simply to charge it up to 100%, instead of just 80%, every two months?
It's weird that they operate 'ideally' between 20-80% but if you don't use 100%, they lose capacity.

Reminds me of the early mobile phone days (yes I am that old) when there was similar palaver in caring for your phone battery.

 

[vfr400]

Most ebike batteries use top balancing, which is basically an overflow system. By charging right up, the high cells overflow, which lets the low ones catch up. you have to understand the difference between looking after the cells and looking after the battery. The 20/80 rule gives you maximum cell life. Your cells will be perfect, but you'll end up with the battery's charging system not able to charge them if they go out of balance.

 

[LukeJolyon]

Thanks again. So if I very rarely, if ever, need a 100% charge, just sticking to the 80-20 rule and never doing anything else should be fine?

Those who need 100% charges are basically going to find their battery lasts (much?) less longer than mine?

 

[Nealh]

Most battery systems use a generic programmed BMS, this only allows cell balancing at the top end of the cell voltage. Typically this is at 4.15v - 4.2v per cell, if you only charge to 80% which is about 4v eventually the cell groups will stray and balance will affect the batteries efficiency. Having part discharged the battery you don't need to charge it each time if sufficient voltage/capacity is left for your needs, though you should charge to 100% before each ride if you know you are going to run out of capacity or know the voltage level will become very low.
Only a smart BMS can/will allow you to dictate/set the balance voltage level to achieve the 80% for extended cell life/cycle life , how ever if you try this routine with a generic BMS fitted you won't get the cycle life anticipated.

Charging to 100% won't harm your battery much as long as you are going to use it shortly after charging, charging to 100% and leaving in that state for weeks/months on end will eventually cause loss of capacity and cycle life. Lithium batteries are about sound management and usage.

 

[vfr400]

Thanks again. So if I very rarely, if ever, need a 100% charge, just sticking to the 80-20 rule and never doing anything else should be fine?

Those who need 100% charges are basically going to find their battery lasts (much?) less longer than mine?

The 80/20 rule is for single lithium cells, not ebike batteries. The cells have a max voltage of 4.2v and minimum 3.1V. That's a 1.1v range. The 80/20 rule applies to that range, so 80% = 3.98v and 20% =3.32v.

You cannot use that range for an ebike battery because balancing happens above 4.15v, so it would never happen.

 

[Nealh]

Thanks again. So if I very rarely, if ever, need a 100% charge, just sticking to the 80-20 rule and never doing anything else should be fine?

Those who need 100% charges are basically going to find their battery lasts (much?) less longer than mine?

If you were to run two identical batteries side by side and both had generic BMS fitted the battery charged to 100% and used regularly will behave better then the battery only charged to 80% over say short term period of 1 - 2 years.

The battery charged to 100% will always be balanced correctly as long as a cell doesn't fail and the BMS remains good, any cell imbalance from discharging will/should be corrected by the BMS at the balance voltage level.

The battery charged to only 80% will eventually become unbalanced as any cell imbalance won't be corrected, you will act as the BMS and stop charging at 4v/80% but have no way of knowing how the cell voltages are behaving. After time could be months could by a year or two any voltage imbalance will become wider.

The only sensible way to charge to 80% is by replacing a generic BMS with programmable smart BMS.
Or by being able to monitor cells via extra sense wires and manually checking and adjusting voltages, this then becomes time consuming and tedious.

 

[Benjahmin]

The upshot here is, use it - charge it until green light comes on - enjoy it - don't stress about it.
The caveats are ;
Don't charge if you aren't going to use it for a while, charge before use (not always practical).
If you do charge before storage, go out and put a few miles on it (say 10) to 'knock the edge off'.
If you've done a short journey (10 miles or less) don't charge.

Best thing for Lithium batteries is regular use.

 

[LukeJolyon]

Thanks so much for all these replies. And I’m glad it’s not just me - turns out it IS quite complicated. No wonder that manual struggles to provide the right advice!

From this exchange I draw the conclusion I should in fact be charging my bike up to 100% for my morning commutes, though not doing the final hour of charge until I get up each morning and then immediately using that charge. That seems to be a key point - not leaving it with 100% for very long with a 100% charge unless I’m immediately about to use it.

At weekends, fine just to leave it with much less charge (say, 30-70%) and only a little use.

I’m also thinking I don’t need to run it down to 5% deliberately as I thought (can’t seem to get it right to zero) but use as above without worrying about needing to do anything special every once in a while.

Does that sound right to seasoned Ebike users?

 

[Nealh]

That's about right Luke, use it or lose it and manage the battery regime.
It is not necessary to be so strict with the 100% charge/usage window to the exact hour a few hours 6 - 12 won't do much harm.
Keep charging to simple regime and only charge if under 80%.

My weekly commute/errand bike I charge the batt (36v) to 100%/Green charger light and use it till I see one LCD bar ( 4 segment scale) is left which is about 25%, at this point I know voltage is approx. 35 - 36v so I know if need be I can get up to another 10 miles from my 5yo battery.
This battery is used alternately with another identical one both the same age and both have about the same capacity, currently I expect another 1- 2 years use out of them possibly more.

You can charge to 80% a few times ( 4 or 5 ) but remember every now and then to carry out a full 100% balance charge to prevent cell imbalance.

100% charge is ok for a short period but not long term.
Over night or a day or two will be fine, over winter for months on end not so good.
The running voltage down to 5 -10% is only needed if you are out on a longish ride and have no option but to run low, even at it's lowest voltage about 3.2v per cell the BMS will hit lvc and prevent a deep discharge.

My other bikes which don't get used as much I leave the batteries at 3.7 - 3.85v per cell for storage and check them every now and then to ensure voltage hasn't dropped.

 

[LukeJolyon]

Thanks Neal - really appreciate your time on this.

Very useful forum to have joined!