Shit check out the 12s4p for 339
The base price is for US18650V3 cells however. They have a 10A discharge rate = not enough at 4P. Changing them to high discharge rate batteries costs 2€ per cell = you need to add 1242€ = 96€ to make it ready for esk8s.
Ah , so the 18650 batteries @barajabali built me are 20 amp? I know they are 12s4p which would equal out to ten amp unless it’s a different 18650 cell
He is probably using samsung 25r with a 20A discharge rate.
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Check these out, pretty penny. https://batterybro.com/products/samsung-25r5-green-inr1865025r5-2500mah-20a With this recommended from @whitepony http://www.groetech.de/index.php?main_page=product_info&cPath=5&products_id=639
Whitepony I have a 42v charger similar to your Evolve charger. You mentioned yours charges to 41.4V I believe ?,…mine charges to 42.2 …if i leave it to fully charge . I wonder if i can modify it to charge to 41V ??
Thanks for this writeup @whitepony ! I’ve looked a few times for configurable chargers and BMSs. Charging to 4.1V has the added benefit of reducing the risk of the full battery/regen shutoff that VESC is prone to. It looks like the BMS is configured at the factory and made to order, but the small chargers are user-configurable.
About the chargers (translated): The final charge voltage can be adjusted at a potentiometer inside the unit to between about 40.5 and about 43.0 volts . If necessary, also to 46V , please inquire. Opening by removing the rubber pads of the feet . Caution : Such manipulations done but at their own risk , may be done only with appropriate expertise ; also voids the guarantee.
my charger arrived, 4A 42V version for 70€ which I now “modded” to 40.5V!
basically you remove the rubber feet, open the 4 screws and youll find a small potentiometer, that was covered in some form of loctite to fixate it.
i then had my half empty spud battery and connected it - 4A charging is really fast - I quickly got to 40.5V and started dialing the potentiometer. apparantly you turn it right for lower cutoff and left for higher cutoff. I slowly dialed right until the charger led switched to green, unhooked battery again, hooked the charger up, it kept green. unhooed battery again, dialed cutoff a tiny fraction larger, hooked up battery and 5min later led switched from red to green, still at pretty much 40.5V.
then I covered the poti with some loctite and put the charger back together.
Im really happy about this!! 
charger hooked up to battery, measuring voltage parallel, led just switched to green!
reapplied some loctite:
manufacturer is “modiary”, maybe someone finds it cheaper on alibaba or so:
p.s.: this seems to be the one I got: http://m.alibaba.com/product/60451408649/Electric-Tool-Lithium-Battery-Charger-42V.html
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That is great ,… my charger overcharges to 42.2 V so this is a great option !
Is 4A charging for your 10s4P ?
? Link does not mention Ajustable max Voltage ?
i assume its this one from alibaba after opening up the one I bought here:
you cant really advertise it as “adjustable” imo. adjustable for the average joe consumer means there is a knob on the outside enclosure. this is more like a mod thats not meant to be, but possible because markus gröbe from groetech tried it out.
he is a superchilled guy btw, we talked for 30min over thw phone about batteries and he said that he has no bms in his batteries either. basically we gave each other mwntal high fives the whole time. 
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Thanks bud !!,…makes me wonder if all chargers have a poti iside for the manufacture to fine tune final Vomtage ??
Think i will open mine just to check ??
Another method to charge your batteries (for bulk charging with BMS) is to buy a MeanWell (or Chinese ripoff power supply) and modify it by adding a potentiometer. It’s sometimes called the R33 mod. Here’s an old forum link: https://endless-sphere.com/forums/viewtopic.php?f=2&t=42793
I’ve done this with the Chinese clones; it’s a different resistor but it works just as well.
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i checked my evolve charger already before ordering and it didnt. think its just a very lucky find by groetech!
that manufacturer seems to supply for pedelecs and hover boards. think it was just a cheap way for them to supply different end of charge states for different manufacturers of e-vehicles/tools. not everyone wants to charge to 42V, but insteads wants to increase lifetime!
I have the meanwell 48volt and its adjustable without having to mod it. Nice but finicky and for a couple more bucks there’s better ones
This is a nice one for the car
But if u get a bulk charger it can’t be for lead acid!!! Don’t remember why.
Adjustable current as well? Usually the default current limit is ~130% of the rated power, and the PSU ends up getting fried without the mod.
It has a potentiometer tiny screw that adjusts the voltage and the current follows. It’s been good and if it is pushed to its max of 400watts too long it slows down and I have to twist the little screw
Here’s a whole slew of stuff from tiny to gigantic.
All 48 about (12s)
http://www.trcelectronics.com/48-volt-power-supplies-chassis-6.shtml
How do cells respond to charging or discharging when they’re in series and unbalanced? Does it further distance them or suck more from the weaker? I do the bulk charging and monitoring/balancing and have found stuff stays close a
Ah, that’s the voltage control. Be careful with that. But then again, with a 400 watt power supply you might not need to worry about maxing it out haha.
LiPo cells vary in both capacity and internal resistance, and both factors determine how much power is actually used from each cell. Meaning that it “distances them further” and does not “suck more from the weaker” in a series configuration.
In a parallel configuration, the opposite is true. If one cell is a bit over discharged, the other cells will actually charge that cell, meaning it will “suck more from the weaker”. There are more risks associated with parallel charging/discharging though.
I’d thought parallel was safer in charging and discharging as any cells that were out of balance are not sucked from but leveled by the parallel cells. No cell can get its voltage above or below its paralleled cells so no risk of it dropping too low or high
In series since the current is forced through every cell I can imagine a cell with higher resistance will get warmer and maybe some energy that would be going into that cell is lost and unbalancing could happen that way but how could series cells become unbalanced. And on discharge the higher resistance cell will get warmer and waste and maybe it snowballs…warmer increases resistance and less current can flow
What if one of your cells went kaput? Then all of your other cells would get drained, and they would go kaput as well. Tesla solves this problem by putting a fuse on each cell, and in case a cell accidentally shorts, the fuse blows, and saves the rest of the cells. I’m not saying it’s unsafe, I’ve done it before, you just really need to understand the risks and proceed accordingly.
That’s pretty much how it works. The internal resistance introduces a voltage drop as well, which means that the cell won’t get charged as much. And the same thing happens when you charge them.
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What does happen if one of ur parallel or series cells goes kaput?
(Kaput being a state with low ability to hold a charge, greatly decreasing the energy it could hold, and if charged solo it would hit max charge and max discharge faster than a healthy cell)
My guess is…in a parallel arrangement all cells must have the same voltage so…yea all the cells in parallel would have their voltages dropping quick on discharge and raised quickly on charging. Not dangerous but less of the parallel cells capacity would be usable even though all those cells would be good. Safe but lame storage performance from pack
In series…a kaput cell is going to be forced to low and high voltages and dangerous but won’t decrease the pack performance really. What u think?