Question about the 80%/20% rule for battery maintenance in winter

KenS

Member
It looks like I will not be riding for the next couple of months, and so I am in battery maintenance mode. The usual recommendation is charge the battery to 80% (or 75% or 90%) and let the charge dissipate to about 20% (or 25% or 30%) and then recharge to 80%.

What I don't follow is how you recharge the battery to 80% (instead of full charge), especially if you are doing the charge off the bike.

Are people doing a time rule (4 hours is good enough) or some other technique to hit that magic 80%?
 

dodahman

Member
You can use a volt meter to see how far along the charge is. There are tables on this site. Turn off the charger, let it all sit for a while, then measure the voltage.
 

rich c

Well-Known Member
Time depends on the size of battery pack, and charger size. My understanding is that you want to keep the battery around 50%. The 80/20 rule is for general use.
 

PaD

Well-Known Member
It looks like I will not be riding for the next couple of months, and so I am in battery maintenance mode. The usual recommendation is charge the battery to 80% (or 75% or 90%) and let the charge dissipate to about 20% (or 25% or 30%) and then recharge to 80%.

What I don't follow is how you recharge the battery to 80% (instead of full charge), especially if you are doing the charge off the bike.

Are people doing a time rule (4 hours is good enough) or some other technique to hit that magic 80%?
I’m doing it by a time rule and using a simple cheap timer. I have a 4A charger and a 604Wh ( or 16.8Ah) battery. My charger gives me around 23- 27% in an hour but your charger/battery combo can of course be faster or slower. The charging is slower ”at the top end”. You’ll learn.
This is how my timer looks. I’m sure you have similar in the US.
43414
 

mrgold35

Well-Known Member
I would also store the battery inside the house if your garage or storaga area gets 40s-30s or less.
 

Browneye

Well-Known Member
Cooler temps are not deleterious to li-ion batts, heat is. I wouldn't let them freeze, and bring them in to room temp for over about 90*F.
The self-discharge rate for li-ion batts is very low, you should not need to do anything for several months. Just charge it up when you're going to ride it again.
50-60% SOC is good for storage. Your BMS will cut off power at low-voltage, its not a problem to fully charge it to ride your bike.

You're making this way more complicated than necessary.
 

mrgold35

Well-Known Member
Really? The battery is that sensitive to going below 50F?
It is usually dry and I can ride all year in NM. Temps can get in the teens/20s in the morning and 40s-60s by afternoon. Don't want to limit my range with 50% charge with a cold battery at 20-30 degrees when I decide to ride to work. I even see about 10%-15% drop in mpgs with my two hybrid cars with very cold temps with the vehicles garage kept (50s-60s in garage with outside temps in teens/20s).
 
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PatriciaK

Well-Known Member
As mentioned above, the 80/20 "rule" is for active use. For storage, my manufacturer (Giant) says 60% - yours may be different, but 50 -60 seems to be the ballpark.
 

6zfshdb

Well-Known Member
Many batteries are compatible with smartphone apps that, among other things, give you voltage and percentage of charge remaining. It might be worth checking if you have a smartphone. These apps are usually free and would be the cheapest solution.

The most expensive approach would be to buy a Grin Satiator charger which is programmable.

The simple timer mentioned by PaD is probably the most practical option.

More information is available in this thread:

 

Thomas Jaszewski

Well-Known Member
Many batteries are compatible with smartphone apps that, among other things, give you voltage and percentage of charge remaining. It might be worth checking if you have a smartphone. These apps are usually free and would be the cheapest solution.
Our complete line of batteries are D-Powercore BT built by EM3ev. A great step forward!
 

Browneye

Well-Known Member
It is usually dry and I can ride all year in NM. Temps can get in the teens/20s in the morning and 40s-60s by afternoon. Don't want to limit my range with 50% charge with a cold battery at 20-30 degrees when I decide to ride to work. I even see about 10%-15% drop in mpgs with my two hybrid cars with very cold temps with the vehicles garage kept (50s-60s in garage with outside temps in teens/20s).
Plug in the night before - it's ready in the morning.
What are we missing here?
 

mrgold35

Well-Known Member
Plug in the night before - it's ready in the morning.
What are we missing here?
The rover is just my back-up transport to work. I can sometimes ride 5X a week or go serveral weeks without riding depending on weather, work schedule, afterwork errands, how I'm feeling that day, etc.. After +7000 miles in 3 years, I sometimes need a day or two off from riding every once in a while. Bad year for riding from me because I haven't been on my rover since July/19 (a lot time out of town).
 

Thomas Jaszewski

Well-Known Member
I have a couple of batteries that have been horribly abused. When I break it down they cost me $75 a season. All this preoccupation and taking the piss regarding getting more charges can become nothing more than a soap opera. Go for a ride. There. Now you feel better?
 

Browneye

Well-Known Member
So you're wanting to know what to do while storing the bike should you need to ride it without forethought?
If it were me I would keep it charged to something in the 75% range so it's ready to go. Even if you plugged it in first thing, anticipating riding it, an hour charge would get you really close to capacity.

A battery with BT interface would be really handy for being able to monitor charge state by voltage. Even so, if you have bar-meter or similar, you could leave it at 4 out of 5 or something similar. Should get you down the road for a couple of dozen miles anyway.

The 80-20 thing is for targeting the ultimate in battery life, but for the vast majority of users it's just not going to make that much difference. Charge it halfway if it's empty, don't store at full discharge or full charge, and you're good to go. Don't cook it. Charge it up when you're going to ride it. Too many are way over-thinking this.

EDIT: Ah, Thomas beat me to it... 😇
 

PaD

Well-Known Member
Too many are way over-thinking this.
I may be one of those over-thinking but this is how I think about the 80-20 rule. (which is still believe to extend battery life?)

I don’t find it taxing to stop charging at around 80%. It’s easy with a timer.
It’s not just a matter of me being unwilling to buy a new $1.000 battery but of course I want my battery to last for a long time.
I want my battery capacity to stay on top as long as possible so that I have the same range over a longer period. I don’t know how fast batteries degrade but I want to postpone the day that I may have to reduce the distance I can go on a full charge.
Charging to 80% is luckily for me very often enough for a day ride. Not always so sometimes I give it a full charge (and also balance the cells I hope )
But I like a fully charged battery. The difference in power is noticeable :)
 
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Browneye

Well-Known Member
I may be one of those over-thinking but this is how I think about the 80-20 rule. (which is still believe to extend battery life?)

I don’t find it taxing to stop charging at around 80%. It’s easy with a timer.
It’s not just a matter of me being unwilling to buy a new $1.000 battery but of course I want my battery to last for a long time.
I want my battery capacity to stay on top as long as possible so that I have the same range over a longer period. I don’t know how fast batteries degrade but I want to postpone the day that I may have to reduce the distance I can go on a full charge.
Charging to 80% is luckily for me very often enough for a day ride. Not always so sometimes I give it a full charge (and also balance the cells I hope )
But I like a fully charged battery. The difference in power is noticeable :)

I completely understand. However you need to understand that you may be talking about a difference of 5 to 10 percent, give or take what degradation you're going to get regardless. So for the average bike you're talking a couple of miles. If that's the difference from making your trip or not you're cutting it too close in the first place, which it sounds like you're not. It's rather akin to putting 10 gallons in your car gas tank and calling it good. I'm okay with that as well. But when I have a big trip I fill it all the way up.

Most of the batteries are costing half or less than that. Surely yes some proprietary types are upwards of a grand. Also know that domestic rebuild shops are popping up with will be able to install new cells in your pack for much less than a replacement.

So sure, putting it on a timer is fine if you want to walk away, I get that too. But it's just a best-guess charger time to target your SOC anyway. You may or may not even be close to your intended target.

What we're saying in a round about way is that it's a lot of machinations for very little ROI on the effort. YMMV And of course you can do whatever you want. I'm a big-picture guy, and while detail oriented, I have way too many irons in the fire than to worry about extending my ebike battery for a couple of miles. In fact, it costs me about $50 to write this reply. 🤣

It may well be that my concern is tempered with my frequency of charge cycles - I'll be lucky if our bikes see 50 of them in a year. So it's gonna take ten years for me to reach 500 charge cycles. Hell, I may well be dead by then anyway.


Now generally as far as these power packs go, look at it this way...
Do y'all have a cordless power tool of any sort? Drill motor, saw, dust-vac, etc.? Or your cell phone, laptop, or tablet?
They all use lithium-ion batteries. I chose my iPhone 6-plus for it's battery capacity - large form-factor means large battery. I just plug it in to charge every night, regardless of it's SOC (state of charge), unless it's above 80%, then it will likely get me through the next day. After four years it is still at 90% capacity, and I think Apple knocks them down some just with OS updates to encourage users to buy new. Plus you can buy a new battery for them for less than $10, are relatively easy to install. Replacements for laptops and tablets are not generally a huge investment either - if they won't hold a charge well any longer just get a new one.

Same for my dust-buster - it sits on it's charger 24/7 unless I use it, then sometimes it will run out to empty and quit, put it back on the charger-mount. It really doesn't care, it's always ready to go when I need it.
My power tools will lose some capacity over several years because I pay zero attention to their SOC. I use them 'till they quit, then put the battery on the charger and charge them all the way up. I think I've only replaced one cordless tool battery over the years, and that is likely from just simply failed cells. The rest of them just keep going and going and going.

If these were lithium-polymer, of which I'm even more familiar, I would be a lot more adamant about battery care - they are nearly explosive if not properly cared for. But Lithium-ion batteries are really stable, are charged at a very low rate, have no memory effect, and don't blow up if you charge them all the way up.

Don't worry - be happy. Charge up your ebike and go enjoy it. If you're worried about it, throw $10 a month in a 'battery fund' to buy a new one a few years down the road when it no longer performs satisfactorily. It's going to take a long time before it won't do the job any longer, unless it's just junk to begin with. Yes, some of them are rather expensive. My bet is we'll see costs coming down over the years, and dramatic performance improvements, and your ebike today is very likely to be completely obsolete in a just a few short years.


There. My worthless 2cents on the subject. I'm going riding. 😇
 

PaD

Well-Known Member
@Browneye
Thanks for taking your time to write all this
I actually read it all.
I must admit that I don’t know how much it really matters to charge the way I do.
We’ll see in the years to come:)