Need help selecting the right battery.

I am building a mongoose Xr250 With a 36volt 9c rear hub motor from E-MTB

http://e-mtb.com.au/index.php?main_page=product_info&cPath=86&products_id=251

What battery pack do you recommend?
http://www.pingbattery.com/servlet/the-8/lifepo4-lithium-phosphate-iron/Detail
http://www.bmsbattery.com/packs/624-48v-15ah-lithium-ion-alloy-shell-ebike-battery-pack.html

Both batteries apear to be equal minus the price and the weight.

Thanks.

You match the battery pack to the controller. Yours is a 40A controller, so get a battery pack with at least a 40A output rating. The ping battery has a 2C max rating afaik, That means a 10ah pack can provide 20A, a 15ah pack 30A, etc. If you only want a 10ah battery pack, then it should have a 4C rating as a bare minimum. Personally I wouldn't use either of those battery packs. Neither will provide the power you need. If I had to choose, I'd get the one from bmsbattery simply because of the specs.

Brilliant! Batteries are confusing!

I wish there were more how to's on using power tool bateries. I own power tools and wouldn't mind using the batteries I already have or even having more. I have 2ea Milwaukee M18 4 amp hour batteries. with 4 that could give me a 36V 8ah battery right?

With 8ah, you need a 5C battery for your controller. I don't know the C rate of those battery packs.

The ping battery can't give enough current. The BMSB one can, but 10aH won't take you very far. LiFePO4 batteries are heavy for their capacity. You should consider a lighter type like the Em3ev ones, lipos or one of these, which is 75% the weight and 50% more capacity than the LiFePO4 one:
http://www.bmsbattery.com/packs/622-36v-15ah-lithium-ion-alloy-shell-ebike-battery-pack.html

I would pick neither.

Take a look at EM3EV. This pack fits inside the triangle: http://em3ev.com/store/index.php?route=product/product&path=35&product_id=160
Furthermore, you can choose the 16.5Ah version. For an output of 30A, it would mean a discharge lower than 2C, which is perfect for maintaining your batteries.

Consider going 50V as well. Much wider choice of batteries, and your 9C will love it.

The problem with BMSBattery is their postage often outweighs the price of the product, a least when shipping to Australia anyway (I bought a 72V charger from them once).

Definitely make sure you get a battery that can comfortably provide the maximum current that your motor+controller may draw. A friend of mine bought a 48V 20Ah Chinese duct-tape style battery off eBay, pouch cell, rated at 1C. He constantly drew up to 35A on it (throttle-happy) and now it only delivers about 13Ah at a 1C discharge rate after about a year of use. Shame.

Since the price of the batteries often matches or outweighs the cost of the controller and motor, it's worthwhile to invest in a quality battery.

If you get further into e-bikes, you may end up building/owning more than one, and if you have one battery that can fit/power them all, you're laughing

Are you

hjns said:

I would pick neither.

Take a look at EM3EV. This pack fits inside the triangle: http://em3ev.com/store/index.php?route=product/product&path=35&product_id=160
Furthermore, you can choose the 16.5Ah version. For an output of 30A, it would mean a discharge lower than 2C, which is perfect for maintaining your batteries.

Consider going 50V as well. Much wider choice of batteries, and your 9C will love it.

Click to expand...

Can I use a higher voltage battery? My the motor I ordered was a 36v 9c; my assumption is I need to use a 36V battery.

The controller you bought will support up to 63V max charge. The motor doesn't care if it's 24V or 124V as long as W doesn't exceed what it can take. Dogman has burnt a few of them up and could give you an idea on that.