How low do you let your battery voltage go before you fully charge it?

[AZOldTech]

I've seen people say that they do not let their battery go below 3V per cell (for 13s 48v battery that's 13*3=39V; for a 14s 52V battery = 14*3= 42V). However some BMS low voltage cut off is higher than 3V. Others use 3.2V or 3.3V. And yet I've heard others use as low as 2.7V.
And yes I do know that is somewhat variable depending on the type of battery and chemistry you are using. However I'm trying to come up with some minimum standard that would be acceptable for the vast majority of batteries. And 3.2-3.3V per cell seems to be the number that I heard more often (41.6V for 48V batteries and 44.8 for 52V ones).

So I'm looking to find out what most people use as the lowest volt number that they will never go below before a full charge (irrelevant if that means 80% full charge or 100%).
Thanks.

 

[AHicks]

A lot of controllers are going to make that "do not go below" voltage decision for you. They're set up to shut down at that voltage to protect the battery. That's where I see the 3.2-3.3v value used most often. Others have a similar feature, but you have more control over what that number is with an adjustment possible.

With the KT series of controllers, using an LCD3 display on 48v, standard/default cut off voltage is 40v (3.07v). You are able to customize that from 38v to 41.5v (2.92v - 3.2v) for drop dead, controller is going to shut down at, voltages.

From a techie/casual rider's viewpoint, I'll try to charge when the battery get's down to 48v (3.7v), and try not to go below 45v (3.46v). Exactly what I'm going to gain by that caution is anybody's guess. I remain unconvinced anyone knows for sure..... despite what's been written. Because you read it on the internet does NOT make it true. -Al

 

[ebikemom]

Probably I'm like many ebike riders who don't go by voltage, but charge when it is "low," or too low for my next day's needs. So if I have a light use day and it doesn't need charging for the next day, I don't charge it. But, if I've had a commute or longer recreational ride, I will charge it. Instead of charging fully, I stop shy of that, by using a timer. I've gotten pretty good at looking at how many bars are left and figuring how many hours to set my timer for. I also keep a charger at work just in case I forget to charge it enough for the round-trip to work the night before.

 

[Volt_Ampere]

I don't go below 3.5V on mine. It drops rather quickly there so you don't gain much range by going lower and your batteries will last longer if you don't discharge them below that. I also don't charge to 100% all the time. I do so sometimes to get the BMS a chance to balance the pack.

 

[glenmorenee]

I haven't tried measuring the battery itself, I just go by the bars and the remaining assist available. When it is down to 2 bars and the range is single digit for either Eco or Turbo, I charge the battery. I have only charged it about 5 times. The first few charges I cut it off at about 5 bars. Knowing about how long it would take to do that, lately I have been letting the charger go to auto-shut off and then unhooking the charger shortly thereafter.

 

[harryS]

Bike controllers, at least mine, are set for about 3.1V/cell for the lower limit. Battery controllers, at least the ones where I've looked at the specs, are set for around 2.5 volts, the lower limit of a lithium cell. The bike manufacturers are looking out for us by setting the cutoff that high.

Since bare cells are rated at their 800-1000 cycles when tested down to 2.5V, that means most of us are already being nicer to our batteries than we realize. If you charge to 90%, then you are doing even better.

If I can plan it right, we'll use about half the battery and then go for a recharge, but there's no harm, I feel, in occasionally running til the controller winks off. I do charge most of my batteries to 100% if I know they will get used right away. If not, I'll leave them uncharged.

We were in Florida last month with our ebikes, and we came home with the batteries all down from our last ride. Will charge them up next month.













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[Volt_Ampere]

Ideal storage voltage where cells age the least is about 3.85V per cell. If you go much below that you should charge right away up to that if you are not going to ride right away.

 

[ebikemom]

We were in Florida last month with our ebikes, and we came home with the batteries all down from our last ride. Will charge them up next month.

My bike dealer said to keep it charged between 30-70% when not riding again soon.

 

[elliot friedman]

When talking about a dormant period for our batteries, are we referring to:

a few days,
a week,
a month,
a month plus?

I've also read in various places to top it off after every ride. Lots of grey area regarding this topic.

 

[AHicks]

"Dormant" pretty subjective, but I would use a month.

My riding consists of rides of all kinds of duration. From a mile (or around the block) to 20+ miles. Because there are so many shorter rides, I just got in the habit of watching my batt voltage as I get off the bike. If it's below 47 or 48 volts, I charge it. The longer runs are generally not as whimsical. They are more something that are planned at least a day ahead of time, allowing plenty of time to charge the battery, no matter it's current voltage.

Agree on the pretty grey. Battery power still in it's infancy to my way of thinking. There's still not as much practical knowledge as there is they way it "should" work as indicated by charts - which may have questionable origin or logic behind them, but only time will prove that.

Bottom line, I took the time to educate myself on these batteries, to a certain extent anyway (still open to new info). This has allowed me to sleep well at night regarding how my batteries are used and maintained.

 

[Snookguru101]

Bike controllers, at least mine, are set for about 3.1V/cell for the lower limit. Battery controllers, at least the ones where I've looked at the specs, are set for around 2.5 volts, the lower limit of a lithium cell. The bike manufacturers are looking out for us by setting the cutoff that high.

Since bare cells are rated at their 800-1000 cycles when tested down to 2.5V, that means most of us are already being nicer to our batteries than we realize. If you charge to 90%, then you are doing even better.

If I can plan it right, we'll use about half the battery and then go for a recharge, but there's no harm, I feel, in occasionally running til the controller winks off. I do charge most of my batteries to 100% if I know they will get used right away. If not, I'll leave them uncharged.

We were in Florida last month with our ebikes, and we came home with the batteries all down from our last ride. Will charge them up next month.













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Don't leave your battery dead for a month before you charge it here is lithium ion batteries like to have juice in them

 

[Gionnirocket]

I've seen people say that they do not let their battery go below 3V per cell (for 13s 48v battery that's 13*3=39V; for a 14s 52V battery = 14*3= 42V). However some BMS low voltage cut off is higher than 3V. Others use 3.2V or 3.3V. And yet I've heard others use as low as 2.7V.
And yes I do know that is somewhat variable depending on the type of battery and chemistry you are using. However I'm trying to come up with some minimum standard that would be acceptable for the vast majority of batteries. And 3.2-3.3V per cell seems to be the number that I heard more often (41.6V for 48V batteries and 44.8 for 52V ones).

So I'm looking to find out what most people use as the lowest volt number that they will never go below before a full charge (irrelevant if that means 80% full charge or 100%).
Thanks.

I have my controller Low Battery Cutoff set to 39v using a 48v battery which is down to approximately 22.5% of total allowable according to Samsung specifications. So down to 3v where Samsung specs 2.65V per cell low V cut off.
I feel this adds a bit of protection to the battery but isn't too restrictive if I find myself in a situation where I need it.
That said. . . as I ride I rarely allow it to drop below 45V as I can easily stay between 50 -90% for my typical needs and only have to charge 1 - 2 per week
I don't think there is a correct number here as you have to weigh convenience, battery capacity and your riding needs. If I needed more capacity per ride to make my bike useful or more enjoyable... I would do so without hesitation.

 

[Gionnirocket]

Don't leave your battery dead for a month before you charge it here is lithium ion batteries like to have juice in them

I concur. . .

 

[harryS]

Zombie thread (two years old), but my batteries were not dead. Controller shuts off at 20%. Add a cold Illinois winter, and no harm was done leaving them sit in my garage when we got from back Florida. We hit -23F on January 30, 2019, probably -10F in my garage. At that temperature, the rubber cords on my chargers would have cracked if I had tried to mess with them.

BTW, shipping regulations often specify no more than 30% SOC.

 

[Gionnirocket]

Zombie thread (two years old), but my batteries were not dead. Controller shuts off at 20%. Add a cold Illinois winter, and no harm was done leaving them sit in my garage when we got from back Florida. We hit -23F on January 30, 2019, probably -10F in my garage. At that temperature, the rubber cords on my chargers would have cracked if I had tried to mess with them.

BTW, shipping regulations often specify no more than 30% SOC.

Not a very good idea to charge at those low temperatures either. Best practice is battery and charger should be near 70° F to charge.
BTW, shipping regulations are not manufacture specifications