Help! Cheap eBay batteries?

[Lj123]

I plan to build an ebike soon using a generic hub motor kit, I would like to keep it on the budget side and I am fairly smart when it comes to electronics so I thought building my own battery pack from 18650s seemed like a good idea however I stumbled across these battery packs on eBay:

1800 -20000mAh Durable Rechargeable DC 12V Li-ion Battery Pack for CCTV Camera | eBay

12V 20000mAh 153 74 36 (mm). 12V 1800mAh 78 45 20 (mm). Short circuit, leakage protective, safety, no need to worry. 12V 3000mAh 84 54 20(mm). 12V 4800mAh 95 55 20(mm). 12V 6800mAh 111 54 17(mm). 12V 8000mAh 125 63 22(mm).

rover.ebay.com

They are only £25 for 20ah @ 12v so for 4 of them in series a 48v 20ah battery pack it would only cost £100!
Obviously I’m skeptical but I can’t find much about them in terms of use with ebikes on the internet so I came here to ask, i can’t seem to find any continuous output values on the product page either so it may be that.
Any answers would be appreciated (this is my first post here) thanks!

 

[sjpt]

CCTV camera use would be designed for very low output power. The cells would probably quickly die under e-bike use.

 

[Lj123]

CCTV camera use would be designed for very low output power. The cells would probably quickly die under e-bike use.

Thanks for the reply!
Yeah I assumed it would be to do with the output power, suppose it’s back to the 18650s!

 

[vfr400]

According to their size, they must be 4S3P configuration. That means that 3 or them would make 12S4P configuration, which is 44v, not 36v. Therefore, you need a motor controller that is able to be configured for 37v low voltage cut-off. A 36v controller will have it at 31V, which is too low for 12S. Also, intermediate voltage batteries, like 44v, can confuse some controllers because they try to guess that it's either 36v or 48v and adjust their settings accordingly.

The next problem is that it doesn't look like there's a BMS. If there is one, it won't be able to deal with typical ebike currents, so at the very least, you'd have to strip them down and wire in a proper BMS.

Finally, you've no idea what cells are in them. They might even be recycled cells. Even if you were able to make a battery out of them, it would most likely be very saggy and not have anywhere near the 20Ah they say.

The most important thing is that you need a battery appropriate for your needs. Don't think that you can knock up some cheap thing then ride around at 30 mph with your 1000w Voilamart kit. Cheap batteries are fine if you just want a bit of assistance and don't weigh too much.

First decide what you want your ebike to do, then choose a motor that has the right characteristics for those, then choose a controller that will provide the right amount of power to meet your needs, and finally a battery that can provide the power that the controller demands. It's all about power, not voltage. Power =voltage x current.

 

[Fordulike]

Unfortunately with batteries, it really is a case of 'buy cheap, buy twice'. If you make the wrong choice at the beginning, you will regret it, especially with higher power set-ups.

I know these are out of your present budget, but any one of the 48v batteries from this supplier will be good for up to 1000w. Well worth saving for!

http://eclipsebikes.com/index.php?cPath=30_31&osCsid=17bf2a73b06b6a19ef28a72b1af091c2

 

[Lj123]

Thanks for all the replies, I’ll make a custom pack from some new LG or Panasonic cells and a 13s bms, seems like the best bang for my buck. Didn’t think I could trust these anyway just checking to see if anyone would have had any success with them.