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Battery longevity question. Charge to 80, 90, 100?

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    Battery longevity question. Charge to 80, 90, 100?

    I was wondering what the best practices are for battery longevity.

    I've heard that it's better to charge your battery to just 80-90% to increase the number of charge cycles / lifespan of the battery. But I've also heard that that is only the case if you're leaving the battery in that 100% charged state for an extended period of time. That if you are using the battery regularly, it's fine to charge it to max and you won't shorten the life. Any thoughts?

    I've also heard that occasionally, you should charge to 100% and leave it on the charger for several hours so the BMS can balance the cells. This should be done approximately 5x per year. I'm not sure if this is really true.

    Also, I have the option to charge at 1,2, or 3 amp (the charger goes to 5 amp but I was told that my battery can't handle more than 3 by the manufacturer, I don't want to risk higher). Is it better to charge the battery faster or trickle charge it? This is for Lithium batteries.

    Are there any other best practices for battery care? I thought this post might serve as a good all-around reference to newbies like myself so we don't diminish the functionality of our new ebike.
    Last edited by Amigo109; 05-21-2022, 07:21 AM.

    #2
    Rule(s) of thumb, at least for me:

    Higher charging finish voltage reduces life cycles of a battery, how much is hard to say

    Leaving a battery at a high charge voltage is definitely hard on them and will kill them given enough time (I've seen this plenty with other folks that didn't realize this)

    Leaving a battery flat for a long time can be equally damaging

    Higher charge currents are harder on batteries too

    Add heat or cold to the mix and that will accelerate the previous issues

    If I know I'm only going use half to maybe two-thirds a full charge no reason not to charge it to just 80-90%

    If I have any doubts I have no problem charging to 100% as long as I'm going to be using it shortly... I'll typically slow charge to 70% well before I'm going to use it and plug it in to take it to the level I'm going to ride with a few hours before the ride, whatever that level is and whatever charge rate makes sense to get it there

    With as much riding as I do 5x a year of 100% to balance would not be anywhere near often enough... rule of thumb would be more like do a 100% charge to balance no less than every five or six cycles

    I also log every ride - which battery (I've got several), which bike (a couple), miles ridden, start/finish voltages, Ah/Wh used, moving time and average moving speed

    I have hundreds of cycles on a couple of batteries and they are noticeably less capable than they were when new in that they have roughly about 10% less capacity and greater voltage sag under load, especially when getting below ~50% and the lower the more they sag which is normal but it's a lot more than when they were new... OTOH this is hundreds of rides, thousands of miles so not sure it's all worth wadded panties from stressing aside from the battery killers (leaving fully charged/discharge and/or high /low temperatures extended time) which are definitely to be avoided

    YMMV

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    • Philip Potgieter
      Philip Potgieter commented
      Editing a comment
      Many thanks! Highly informative

    #3
    I am new to ebikes and want to know how important the break-in period is. I have a Bosch 625 battery on a Bosch motor. The Bosch guide does not say anything about breaking in, although many expert do recommend it....... Second question - may I charge my battery en-route (say when I am half way to my destination? Isnt' the battery hot and will be damaged?

    Comment


    • AZguy
      AZguy commented
      Editing a comment
      If you mean "breaking in" the battery you should definitely do 100% charge to balance for the first half dozen or so times you charge

      One way to look at it is if you monitor the battery voltage while charging (plug a voltmeter into the discharge port), if it takes a long time to complete the charge once the voltage has reached around 100% it most likely means the cells were out of balance and the longer it takes the more out of balance they were so should likely do a full 100% balance charge the next time

      I have some batteries I often don't use for a while and they often sit for a long time (sometimes months) at around 60-70% and they will always take a long time to complete the charge when they sit around like that as I'm presuming they tend to get out of balance when sitting for a long time

    #4
    I thought of another question, how can you determine what % charge is in the battery based on a voltage readout. My display has the option to show voltage, but I don't know how to translate voltage reading into available power left in the battery.

    Also, I was also told to let the battery rest a couple hours after a ride before charging and don't ride immediately after charging. Waiting for it to cool down after a ride seems logical. IDK why it would need to rest after finishing charging.

    I'm especially interested in preserving the life because there is just enough juice for me to make it to and from work on a single charge.

    Sorry for all the questions but im sure this will be helpful to a lot of people. Nice to have a single thread with a lot of info in one spot.

    Comment


    • AZguy
      AZguy commented
      Editing a comment
      Yes, there are charts on this forum and all over (just search) that will give you a rough (it's pretty rough) correlation between state-of-charge and voltage. They are all far from gospel (there are plenty of different versions) so take them all with that boulder of salt but they are good guidelines. The reasons they aren't very accurate as far as true SOC vs. voltage is many. For one it's far from a linear response... it also makes a difference how much they got charged and whether they're in the charge or discharge process... temperature has a non-negligible effect too and most low-voltage cutoffs are set significantly higher than 0%.. different types of cells have different curves too

      To really know stat-of-charge and amp-hour totalizer should be used and good ones can be very accurate although keep in mind that the total amount of amp-hours will vary a little depending the magnitude of discharge current

      I tend to ride very shortly after charging, I don't really think it matters but that's just my opinion and I have a bias since it's what's easiest for me

      I don't tend to charge right after riding but that's because I'm lazy more than anything else and I have multiple batteries so they just get rotated into the mix anyway
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