Battery Capacity Monitor

So here’s the scenario :

You’ve charged your large battery pack to 100% fully intending to go out for a proper ride and drain that thing back to 20% or so in the process… but something stops your plan and you can’t go out afterall. Could be rain, or an emergency that wasn’t even on the cards 4 hours ago when you started charging.

Problem is you don’t use your board daily, more of a weekend plaything, and the next time you’re gonna get chance to ride might be a week or two in the future. Problem is now you’re stuck with a fully charged pack in your garage and got all those worrying advice threads you’ve read in your head telling you not to store 18650 cells at 100% for long or fear damaging the internal chemsity, and therefore lifespan of your pack.

Given that the pack is often one of the most expensive parts of an esk8, how can you get the charge level down without riding it ? Is there a device you can plug into that will safely drain away excess charge back to storage levels ?

I don’t want to spin the wheels on the bench, without any real load, for hours on end to reduce the charge level, but I also don’t want to leave the pack fully charged either.

I’ve got a drone with batteries labelled as ‘smart’ in that if not used for a while it will discharge itself back to 50% storage levels… however these are small batteries unlike the esk8 ones so the internal circuitry won’t be heavy duty or anything.

What are my options here ? Surely there’s a solution but given I don’t really know what it is I can’t search for it !!


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I wonder if there is something you can plug into the charge port that will drain the battery reasonably quickly down to like 80% or so.

some kind of led light?

some boards have usb that can charge phones right? might as well use that energy instead of wasting it?

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I brought a 9W led light from amazon that can run directly from the battery voltage. on my board i run bms with charge/discarge on the same pads so I can plug the light into the charge port to get power from the bms.

In theory a 12s4p pack is around. 500Wh so to use up around 50% should take around 24 hours.

you could just plug it in for a day. Worst case is that you forget about it and the bms shuts it off when the voltage gets low


Evolve brand chargers for whatever reason will float charge my pack between 92% and 97%. It used to make me mad but then realized it’s done to prevent leaving fully charged batteries.

As this is my first real pack, I can only base this assumption off of what I’ve read :man_shrugging:

storing a fully charged board for a month could lead to battery fatigue if done repeatedly, but just a week every blue moon? I don’t think that’s going to be much of a problem, really.

Maybe just leave the board on overnight, you’ll lose 3-4% just from the ESC and fuel gauge taking juice.

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I think about this every time I charge. With having multiple boards I accidentally charged the wrong board the other day that doesn’t even have motors on it at the moment. I just left it on for a day or two and I’m comfortable with it again.

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This is silly. I mean i know its something we have to think about, and the effects of storing at full charge aren’t silly, but i don’t want to stress about my board being at 100% sitting in my garage.

Especially since i’ve left it fully charged repeatedly for days at a time over the last couple of years that i’ve had this same 12S5P

One thing i noticed is that when i leave it on the charger too long it creeps back down from 100% to the high 90s. Maybe that’s the problem solving itself?


Yep. I think it’s the internet scaring me about these batteries. That and the fact that if something were to happen with them I would take the risk of affecting all my neighbors that live in my apartments. I’m conflicted…

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remember seeing a youtube video on jehu’s channel - don’t ask me which one - where he takes shipment of a bunch of cells that had been sitting at 4.2v for YEARS. he does a capacity and IR test, and it’s basically exact to spec. meaning, fully charged had no impact on the cells.

having said that, if you want to discharge your pack, put a load on it. a fan, bulbs, i use resistors attached to a heatsink. but remember to drop the voltage down depending on what you’re using. most fans want 12v, some 24v. bulbs have a whole range of voltages. resistors get HOT so need to dissipate heat somehow.

i use this to discharge, it’s about 6amp @ 50v