is there a way to test out how “good” a li ion battery pack? Found a 10s4p to pick up in person and it looks like its been taken care of great. How can i test to make sure everything is as good as it seems? Should i just take a board and test it? Im a newbie with all this electronics stuff and a man can only read so much in a day… any advice appreciated
You could measure the isr, my iCharger gives me a full readout capacity…
bit of info here:
https://batteryuniversity.com/learn/article/how_to_measure_internal_resistance
Ask how many cycles it has done, charge voltage, the low voltage cut offs used?
I’d test the full charge capacity & the ISR.
Is it a home made battery? I’d ask for build photos (I’m personally suspect on buying a second hand battery) If you are unsure about anything, walk away.
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What he said 
Find out if it’s prebuilt. If it’s diy walk away. Not worth the risk unless you know the builder. That shit will burn your house down. If it’s prebuilt you need to know what it came out of. 10s 4 p is not a usual Chinese config. 2/3/5 seems to be the norm. With batteries you need all the info you can get and if it’s legit you’ll get it.
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Oh its a prebuilt… not trusting anyone who isnt backed by this forum… 10sp3 or 4. He doesnt know much about batteries and only needed a 10s for a diy esc
Im gettin the battery, a remote and a single diyeboard esc for $100 My guess is the battery is allso from diyebrd
Too bad I got a custom battery made by a dude NOT backed on this forum. He seems fine to me and he showed me other packs he build too.
By the way the battery is packed in ductape. Does this work or do I have to replace it
It does, but it is a bit ghetto. Kind of cutting corners, makes you wonder what other corners are cut? 
If it’s flat pack it’s 3p if it’s in a stack it’s 2 or 5. You’ll know it’s the 5. 50 cells is a lump. Look the battery will work and for the money it’s a good start. Just don’t expect too much from it. If you’re going to mate it up with a VESC then don’t go above 12 amp per VESC if dual and 20-25 if single or you’ll blow the bms.
This will be a fourth board to have for friends or family to use. I have a 6374 and mount laying around so 100 for a new build sounds good to me. I can alway find a cheap long board on offer up to convert. I was just going to count the cells when I inspect it
Can’t think of a single thing that could go wrong dude, maybe just store and charge in your shed 
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Oh i meant count the cells to determine if its 10s3p or 4p… i plan to buy some kind of tester like you suggested andd yea… im storing it out back in my wife’s she-shed
Any inexpensive icharger recommendations?