Electric Bikes - A ch eap lithium battery - should I be suspicious?

I saw a battery today that the lbs claimed to be lithium. Actually I have seen it in a couple of bike stores. The selling price was about US$ 130. It was 36 volt and was hooked up to a 240 watt motor. The LBS claimed to be able to about 20 miles on a charge.

This seems to be very cheap to me. Should I be suspicious? I know that there have been several versions of Lithium -xxxx batteries and that the earlier versions had problems - were even dangerous.

What should I think about this?

That does seem exceedingly cheap. Li-Ion batteries can be dangerous if overheated or made with
poor quality that leads to imbalancing: the results can be nasty. I recall a man being killed by his cell phone when it burst within his shirt pocket, it overheated apparently. Dell had a huge problem with batteries in their laptops exploding due to defects: http://www.theinquirer.net/en/inquirer/news/2006/06/29/dell-blames-battery-for-exploding-notebook
that wasn't an isolated incident, there were many more and those batteries/laptops ended up getting mass recalled.

Lithium for that price would be great, i'd just take the time to inspect the battery, see if you can find out who makes it, what its stats are and so on. 20 miles "claimed" seems lower for lithium, so i'm presuming its not a huge battery either, which could be part of the price.

Yeah, I would be suspicious. Especially if they won't tell you what you're getting. Still, if they give the info, you might be able to find out.

Too many details are missing. Such as, what is this battery's capacity? What type of cells is it made of? What kind of BMS does it use? etc. I wouldn't buy it.

thanks! Now that I know what to look for I will start asking questions. I will let you know what I find. But if the motor is 240 watts and the battery is 36 volts the battery should be 7 amps?

The motor is kinda irrelevant, current depends more on the controller. At minimum the batteries have to be able to put out at least as much current as the controller can pass, more is fine.

Say the battery is made of 5Ah cells that can safely put out 3C, that means they should be able to put out 15A. If such cells were setup in parallel they'd give 10Ah, and so at 3C they should then be able to put out 30A.

A 5Ah battery capable of 15A would see shortened life with a 25A controller...

Are these walk-in stores or online offerings? Walk-in would be much simpler to qualify and allow for warranty recourse in the event things go wrong. Don't forget the world of RC hobby - they have strong world/local followings capable of answering many questions regarding battery technology/applications and often sources we've never heard of yet.

When I qualify batteries - I don't even consider anything less than 40amps max discharge per cell. Part of that is due to my work with kick scooters - which demand much larger current draw than an eBike. 100A cells are about all I can safely use for my ESR750 and then only when I limit the controller a bit.

Lithium series strings really need a LOT of monitoring for safe charge/discharge. You must be able to KNOW if/when each cell is getting unbalanced, when it's full/empty and a keen eye on cell temperatures. I have yet to see the Holy Grail BMS and/or monitoring circuit for high power lithium but it's constantly evolving and someday we'll have complete systems that address these concerns.

In the meantime, we're kinda the Guinea Pigs of the industry and we'll make mistakes along the way. If the worst that happens is you have to pedal 100lbs for a couple miles - consider yourself lucky!