A couple days ago I fully charged my 10s4p. Not long after my vesc took a shit and my board is currently useless. There’s a chance I’m done riding for the winter so I can get it fixed and get some upgrades for when summer comes back around, but my battery is still at 96%. How can I discharge it to storage voltage?
Hook it up with crocodile clips to an incandescent light globe
Edit: it might take a while 
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That sounds damaging to the battery lol
You can do this 
Another option would be using an electronic load tester. I picked up a cheap one on amazon. Can drain at a few amps. Just set an alarm so you don’t accidentally overdischarge.
This is what I use:
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It wont damage the battery as long as you take it off before it goes too low
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Some 12v bulbs in series should do the trick. Dont use a household bulb would take a massive amount of time, as the resistance is very high.
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Its fine at that voltage. Storage voltage is more a point of not storing at too low a voltage than too high. It will deplete over time so if you store at a low level it may not come back when its called to duty. Check it periodically over the closed season to be safe.
My test bench pack hadn’t been charged in 6 months and was called into duty when a battery made by a major player who is in a bit of a pickle, shit itself. Its a trooper.
I might just try to bring it down a little. I would prefer to not leave it too high
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Instead of using light bulbs, could I use resistors? If I used ohms law V=IR I could figure out to pull a constant 4 amps I would need 10ohm resistor
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Depending how fast you want to discharge, the resistors would need to dissipate huge wattage (It will burn, or bang lol), so would be very expensive and likely need to be actively cooled. whereas 10x 12v 35w bulbs are £3 total. Plus you would be less likely to accidentally leave them on too long. Im actually going to build my own discharge rig this week, with bulbs and stripboard. Ive been meaning to do this forever. Ill probably have a setup that disconnects as a set voltage too.
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Not entirely accurate. You can actually do some damage to the overall capacity letting it sit there fully charged and depleting over time (months). Generally recommended to let lithium batteries sit between 30% to nominal charge at 3.7 yeah?
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Again that may be completely correct but all I have read is keeping at 30 to 40% to prevent over discharge. I have never seen any actual damage occur from leaving batteries near full over time.
I have a lot of lithium batteries. A lot. Some of which do stay charged up for months on end because I have a little man who does my lawns. I’m so posh.
Just haven’t noticed any issues with leaving them charged up.
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Personally, I’ve seen larger lipo packs left fully charged for months puff up on the first attempt to charge even though they’d only lost about 30-50% charge. Happened enough times to take notice across a number of years. I think capacity loss is also a factor depending on how long it’s stored at full charge.
Keep in mind, my company used/deployed thousands of lipos a year, so it’s entirely possible my observations are skewed simply because of the number of batteries we worked with I was bound to run into manufacturing defects often.
Would be interesting to see some data on this to know what’s within acceptable use vs detrimental.
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+1 for this. There’s actually an uglier but better version this. The purple one above is analog controls with digital display. You twiddle the knobs until the displayed numbers are what you like. The ugly one below is digital controls. You set the numbers and hit ON.
And apparently there are knockoffs lol.
http://www.360customs.de/en/2017/01/150w-constant-current-load-60v-10a-battery-capacity-tester/
It’s worth it, you can set the current you want to drain at, and when to stop. 60v 10a up to 150w. 4 wire sense (compensates for voltage drop across the power wires due to resistance+current). Really useful tool.
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I linked the top one earlier but I guess the OP wants to go a different route. I totally agree though.
Edit: just realized that was a “quote” 
still dusting off the cobb webs from a late night in the battery lab.
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Lipos then all bets are off. I have seen some very interesting behaviour with those. Quite funny you mention that because I charged up my Revo for the first time in about 18 months and 1 battery puffed before my eyes yesterday. Other one was fine. My 2 max amps took a charge no drama but they are good quality cells.
It would be good to have some definitive data to back up experience.
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Hey so that second one is basically the same as far as the load it can handle(about 3A at 12s full)? But it is programmable. Think I might have to give one a try! Super cheap comparatively as well. Good recommendation
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Yeah I got lured by the pretty colors, then found that youtube video. Ended up with both. Pretty one stayed in the drawer until I fried the ugly one. Tried the pretty one, I was like, wtf? Ordered another ugly one.
It’s seriously useful. For balancing p-groups, testing buck converters and power supplies, questionable batteries, storage charge, fusing current of fuse wire, etc etc etc.
Hey @DerelictRobot do you think putting a few in parallel to increase current would work? I’ve wanted to try some nickel strip current handling tests but the 10A max makes things annoying.
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Did you happen to check the voltage on it prior? Was it within norm? If so, that’s the exact behavior I’ve observed dozens of times. We discovered this the hard way when… I shit you not: we received an entire batch of lipos that had been fully charged at the factory for some fuckodd reason. Only about 200 packs in that batch, but they had already sat on a boat across the lake then sat in our warehouse for another 2 months before we noticed.
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