Is it ok to unplug battery from charger before...

YonathanZ

YonathanZ

10 mW
Joined
Dec 25, 2014
Messages
23
Hi,

Is it ok to unplug the battery from the charger before the charging is complete, or does it affect its longevity?
My ebike has a li-ion battery. I charge as soon as I can and never completely drain it but I'm reluctant with charging during the day because I'm not sure if I'll need it in an hour or so (and charging does take a while).

Thanks.
 
It won't harm your battery to get a partial charge when you need a bit more but dont' have time for a full charge.

Example, you ride to a meal someplace, or a visit at a friends. Your battery would be either very low, or not make it at all without an hour on the charger to increase your range. Ride to the meal, charge while you eat, ride home. NO problem.

But if you can conveniently charge completely, do so. Don't go riding multiple trips over several days without fully charging. There is no benefit from draining the battery more before recharging.

Cycle count is what worries many. If you expect 500 full cycles, you'd expect 1000 cycles of half discharged.
 
It might even be marginally better for the battery. depending on the chemistry, batteries do last a little longer when not charged to maximum.

The down side to unplugging before fully charging the battery is that the pack won't have been balanced. The balancing cycle starts only after your pack is fully charged and then left on the charger for a while. Missing the balance cycle a few times in a row shouldn't hurt anything if you're not deep discharging it. But it will need to spend longer on the charger being balanced the next time you fully charge it.
 
YonathanZ said:
Is it ok to unplug the battery from the charger before the charging is complete, or does it affect its longevity?
Click to expand...

Yes, you maximize longevity :D

As far as I know, there is not even one reason in lithium chemistry to have any benefit on charging a cell till 100% (~4.2V). Omitting balance purposes, charging below 4.2V will result in double the max cycles life for each 0.1V less the charge stop (there are extended info about that on an ES thread and outside ES). There are a bunch of other factors that counts on life span and cycles life, but that is what You need to know about stopping the charge before 100%.

Healthy cells but No Charger/Bms High Voltage balance
 
charge whenever you can. do not worry about charging to full charge if you use the pack immediately. just do not leave the pack on the charger all the time or leave it fully charged.

so if you have a chance in the middle of a trip and can charge, do it. it is best to use charge from the top of the pack and not from the bottom, this is where the entire idea of counting charge cycles proves how useless it is.
 
So you're saying I shouldn't leave it fully charged for long? Is a day or two okay (I do that frequently)?
 
The ideal conditions for the longest lasting lithium cells is to store them at around 40% charge someplace cold. Also, charging them to only about 70% capacity will make them last much longer.


But then, whats the point? Your battery is a consumable item. it will last much longer if you store it in the freezer and never use it, but where's the fun in that? Charge it when you can. If it needs to sit for a day before you use it, don't sweat it. Sure, doing that often will shorten it's life some, but you're trading battery life for ebike convenience. The bike is there to serve you, and if you need to buy it a battery a little sooner in order to make the bike fit your wants and needs, then so what?
Charge it to full when you need the range. charge it to full every few times anyway so that it can balance.

The biggest 4 killers of batteries are:
leaving them hooked up to the bike for an extended time so they drain down too far.
Keeping them out in the heat at full charge for an extended time.
Not keeping them balanced.
Time.
 
It's also good to fully charge the battery for the bms to work, it only balance at end of charge. Just don't let the battery get to low and store it as it could kill the battery. It does have self discharge over time.
But yes you can unplug and ride before full charge. I don't like the bms or controller hitting lvc.
 
Absolutely!

This is often referred to as "opportunity charging". If you have access to a three (or two if your not in the USA) pronged outlet in the midst of a ride - stab it.
 
Trying to simplify the above.

Do charge completely often enough to let the bms completely balance the pack from time to time. Hard to say how often, or how long it should take. For a bike ridden daily, I'd say do a complete charge once a week, like let it charge overnight.

How do you know when to stop if you want a partial charge? Get a voltmeter. I often use a cheap (3bucks) led voltmeter to know if I'm closer to half charged, or full charged. Not real accurate, but it will tell me when I'm within a volt or two of finished ok. If you fully charge to 42v for example, you could tell by the voltmeter when you are at 40v, and unplug then.

Ideally, don't leave it laying around fully charged for days. Charge, then ride soon. I sometimes charge intending to ride, then don't. But a short ride will bring the voltage down enough to store overnight with less damage. 1 mile ride at full throttle doesn't take long. A few days later when I do go out, it will only take a short time to fully charge again if I need to.

Stabbing the plug is great. But if you have enough to make it home with lots to spare, why bother? If you need it, for sure grab a short shot of power when you can.
 
dogman dan said:
Trying to simplify the above.

Do charge completely often enough to let the bms completely balance the pack from time to time. Hard to say how often, or how long it should take. For a bike ridden daily, I'd say do a complete charge once a week, like let it charge overnight.

How do you know when to stop if you want a partial charge? Get a voltmeter. I often use a cheap (3bucks) led voltmeter to know if I'm closer to half charged, or full charged. Not real accurate, but it will tell me when I'm within a volt or two of finished ok. If you fully charge to 42v for example, you could tell by the voltmeter when you are at 40v, and unplug then.

Ideally, don't leave it laying around fully charged for days. Charge, then ride soon. I sometimes charge intending to ride, then don't. But a short ride will bring the voltage down enough to store overnight with less damage. 1 mile ride at full throttle doesn't take long. A few days later when I do go out, it will only take a short time to fully charge again if I need to.

Stabbing the plug is great. But if you have enough to make it home with lots to spare, why bother? If you need it, for sure grab a short shot of power when you can.
Click to expand...

Doesn't the BMS balance the pack even when it's not charging? The BMS I bought from Em3ev has a balance current in the specs. I would not charge any battery overnight (on purpose. I have forgotten to disconnect before).
 
Yes, the bms will discharge any too high charged cell when the charger is not plugged in.

Nothing happens, if you have partially charged. The bms finds the overcharged cell, and lowers it's voltage. It will not balance a partially charged pack.

Completely balancing, will require two things. Bms discharging the high cells while the charger light is green, and a charger that will restart later, to continue charging up the undercharged cells.

If your charger is not one that will restart, then you need to let the pack sit awhile, bms working, then plug back in again later to start another cycle.

If your pack is severely unbalanced, it could take many repetitions of this to get completely full.

How do you know? If your pack takes a full charge, and then keeps almost all of it overnight, it got balanced. If it drops some overnight, but plugging in the charger has it run only 2 seconds then turn off, then it's very very close to balanced. If it runs 10-30 seconds, likely it's still working on it.
 
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