Electric Bicycle Battery Choice

Positive discussion on ebikes and pedal assist bicycles

Electric Bicycle Battery Choice

Postby algaematt » Tue May 24, 2011 9:25 pm

I'm interested to know from any experts or users what is the best choice of battery for an electric bicycle. I've been dealing many conversion kits through the years and have plenty of financial woe from failed batteries and am looking to find out anyone who has knowledge on the best type to use for an electric bike. From my testing and experience I've found the following:
Lead Acid - very reliable but very heavy. Also life time is quite low.
Nickel metal hydride - have never tried but I've seen it to be heavy and now seems to be an out of date chemistry
LiMn - extremely light and quite reliable. Well priced from Chinese factories but hard to find them with solid BMS circuitry. Unsure of safety
LiCo - have never tried but reveiws point to it being thermally unstable (I think that Sony had some laptops explode with these a while ago so have given them a bad name, perhaps justifiably)
LiFePO4 - reputably the safest. I was selling many of these but have found the BMS to be quite unstable. It seems that if they work well for a few months then they'll be great but I've had many fail within the first few months. I think that it's a matter of poorly designed BMS circuitry for them that's letting me down. This has led to blown out cells and consequently failed batteries. They also seem to be the most expensive of the lot.
Li(NiCoMn)O2 - I'm now testing some of these that use Panasonic cells. So far so good. They have an excellent power to weight ratio. Still early days but I'd love to hear from anyone who has experience running these batteries with high power motors (500-1000W) or has knowledge of their safety and longevity.

Matt, Solar Bike
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by BNA » Tue May 24, 2011 10:04 pm

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Re: Electric Bicycle Battery Choice

Postby cachexian » Tue May 24, 2011 10:04 pm

Presumably you've read extensively on Endless Sphere forum?

LiCo (is this LiPo) and LiFePO4 seem to be the batteries of choice there?

LiveforPhysics has done a lot of failure testing of Lipos and it would seem that you really have to abuse them to make them burn up. Of course, when you are selling Lipo (or any other battery for that matter) to a customer, you don't really want to be saying to them a whole lot of really complex instructions about charging. The battery supplied to me is a LiPo (or at least that's what the sticker says). I don't know what stuff is happening inside the battery box as far a balancing circuits etc but there is only one plug input to charge the battery so I'm getting the feeling that it's a bulk charging (and not a balance charging solution). I was never warned of any risk of fire...

Have you considered constructing your own batteries, getting your own BMS boards manufactured?

There's lots to learn still for me.

Cachexian.
Scott Sub 40 with 200W, 36v Ezee geared front hub motor
and...
Trek Madonne 3.1 driven by left leg and right leg
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Re: Electric Bicycle Battery Choice

Postby Joeblake » Tue May 24, 2011 10:11 pm

Lead Acid - very reliable but very heavy. Also life time is quite low.


You forgot to mention relatively inexpensive. I can usually squeeze about 2-3 years out of a set of SLA batteries. The only problems I've had were caused by failure/lack of a regulator and they were overcharged.

Joe
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Re: Electric Bicycle Battery Choice

Postby cachexian » Fri Jun 03, 2011 7:38 am

I'm considering making up a new 36v battery pack from Turnigy LiPoly batteries from Hobbyking. I would hope that these will give me less voltage sag than my current battery (supplied by EVS).

With a max 15A controller from a 10Ah battery I'm only drawing maximum 1.5C from the battery but it sometimes sags as much as 3-4volts (measured by my cycleanalyst). The Turnigy batteries are rated at least 25C so I should be able to expect that they will sag less.

This will be a steep learning curve for me since it will involve soldering and connectors etc. but all in the name of fun!

Cachexian.
Scott Sub 40 with 200W, 36v Ezee geared front hub motor
and...
Trek Madonne 3.1 driven by left leg and right leg
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