I know of these 3 options for the BMS for BMI batteries.

BMI VMS

The manufacture of these batteries provides what they call a VMS. It's actually a microprocessor based board that handles balancing and gives outputs for driving external circuitry for over voltage and low voltage protection.  The board they provide is able to monitor 4 cells in series, you can connect multiple boards via a provided port so that you can build up a system to monitor as many batteries as is needed.  The single VMS board is around $50, so for a 36V system you'd need 3 boards so about $150.  This setup is nice since it monitors the batteries constantly and logs over volt, low volt, cycle count and other events into internal eprom.   There is also a serial interface port that allows you to connect you computer and read the stored data. It's biggest limitation is the balancing current which is about 100ma, but since these batteries seem to stay pretty well balanced, it's not usually an issue.  Also, using this option, you'll need either a smart charger or an external circuit to cutoff power due to high voltage and you'll also want an external circuit for cutting out power due to low voltage.   EchoCar has a great write up on this VMS board.  Electric Echo VMS link

PING BMS

Li Ping provides a good solution with a complete board that can be wired directly into the pack.  Their board also comes complete with High Voltage Cutoff so it prevents over charging by cutting the charge off to allow the circuit to balance the pack. It also has a low voltage cutoff circuit to disconnect the load when the battery voltage is too low.  This is the lowest cost solution for a full bms.  Ping sells the complete board (for a 48V pack) for around $50).  This solution is about 1/4 the price of the BMI VMS solution.  However, this is an analog circuit that does not do any logging of data conditions.   Also, since ALL the load current must go through the LVC of this board, you'll need to be sure to request a board that can handle the maximum current you'll ever need to use.  Since the BMI cells can source 200Amp or more and the ping pack is currently limited to about 50Amps, this solution will not allow you to use the batteries to their maximum potential.  A possible solution would be to wire 2-4 of these boards up in parallel which should increase the total load current capacity AND the balancing current.  I haven't tried this yet, but it should work fine.  Li Ping is a very reputable distributor and I've had good dealings with him.  He can be reached by email.  pingping227<AT>hotmail<DOT>com

4-24 - Cell Battery Management System

OK saved the best for last.  Here is a kit that was designed by an endless-sphere forum member to be the best bms available.  It has a completely flexible design that can be used on packs of any size.  It's for the do-it yourself-er.  You'll need to solder it up, but this saves in cost and allows you to create the circuit that you need for your particular application.  You'll also need to get your own components which can save you money if you a lot of parts laying around. 

http://www.tppacks.com/products.asp?cat=26

This electric motorcycle in the UK does 80mph and can go 30miles on a charge using first generation Lifebatts and a Perm PMG-132 motor.  Great ideas here.

Here is an article about the advantages of LiFePO4 batteries over Lead Acid alternatives.  It is well written and not overwehlmingly tehcinal.

http://www.austrol.com.au/index.cfm?menukey=125

By popular demand (and excess stock), I've decided to sell a number of  my BMI LiFePO4 cells. 

I have two cartons of brand new BMI cells available for cost plus actual shipping from TX.   These cells are here in Texas right now and can be anywhere in the US in 2-3 days. This shipment is fresh, directly from the factory in Taiwan just 1 week ago. I've been using these batteries to build bike packs, car batteries and trolling motor batteries. Everyone who has used them has been highly delighted in their products. They will give you years of service and save lots of money over time. I really believe that this product is the best on the market

Just FYI, these cells are able to handle current surges of 200A each! So, you must be very careful how you use them. Fuses are highly recommended. I'm using 6 gauge wire and pallet jack power connectors on my setup.

View Listing on Ebay

Here is an early preview of a 12V Custom LiFePo4 pack we are working on.  Missing from this image is the outer case and terminals.  The outer case will be made from lexan and is extremely durable.  It can be made water proof for marine environments.  The pack is assembled by hand and can be customized to fit the intended use. This pack is able to provide peaks of up to 400 amps of current and has a capacity of at least 20Amp hours. It's powerful enough to be used as a start battery for an automobile or as the drive battery for a trolling on a boat, or even to drive a golf cart.  This pack is based on a highly tested design and is built from the best materials available.  With an expected lifetime of over 7000 cycles, this battery will provide power for many, many years to come. To get more information on the possibility of using one of these packs on your next project, feel free to email me at mcstar@gmail.com.

Here are some pictures of my e-bike with the custom built LiFePo4 battery pack installed.  This machine cruises at speeds between 26-30mph.  I've got a range of 25-30miles.  I ride it to work 4-5times a week weather permitting.  So far I've put 2000 miles on it (since January 2008).  So far, including the bike, I've put about $1500 into the setup.  Figuring at current gas prices, I've saved at least $350 in fuel.

Photosynth (46 pictures)

Yesterday my bullet connectors failed.  I suppose I shouldn't be too surprised, since  they were perhaps the most under-rated part on the e-bike and they take daily abuse.  This connection is made and broken at least twice each day and each time I get a nice big spark as the controller's capacitor chargers. The connecting wires were only 12 gauge so they probably also represented a high resistance connection especially under load.  I suppose it was for all those reasons that I really didn't mind being force to upgrade  them when they broke. 

It seems e-biking upgrades always follow a common pattern.  First you buy cheap because you just want to get started and you're thinking it will save you money.  Then you start putting on the miles and you have something break.  That's when you realize that spending a little extra money up front will save you money and time in the long run and you go ahead and upgrade to the best you can find.  1000's miles later you are still very happy you did it right!   Each day I'm forced to drive my car vs. the e-bike cost me at least $10 in fuel.  So the $30 I spent on this upgrade was nothing compared to driving the car all week.

So, I upgraded both ends of my battery connection  with heavy duty 6-gauge wire and high power connectors.  I suppose it's only fitting since I'm carrying around a $1000 + battery that it should have a high quality load carrying connector.  Now I've got at least 50A of load handling capacity.  I'd recommend this type of setup to anyone with an E-bike once your initial setup fails. I found the connectors and wire at NAPA auto parts.  They had the parts in the back though, not out on the shelves.  Tell them you need connections for a high power battery setup.  These connectors are the kind used in 36V and 48V electric pallet jacks and light duty forklifts. Here's an online source for the connectors  http://www.allbatterysalesandservice.com/browse.cfm/4,642.html

BMI is known for producing the LiFePo4 battery packs of the highest quality.  They have recently started producing and shipping a line of very large, high current LiFePo4 packs built as drop in replacements for hybrid cars.  These packs are made in voltages up to 144V and with current ratings in bursts up to 200Amps per parallel cell!

144V 10Ah pack	3.3V 10AH Individual cells

Purchasing the individual cells instead of packs gives you the flexibility to configuring them into any physical arrangement deemed necessary.  This means however that you're also responsible for determining how to charge and balance your custom pack. 

There is a cell balancing VMS available for purchase.  Each of these circuits can manage the charging of 4 batteries.  They also have a serial output that can be used by external circuitry or a monitoring computer to turn off load when low voltage or over voltage is detected.

Right now the cost per unit on these batteries is among the highest cost of any other cells on the market, but if you are after high discharge current capacity, extremely high recharge current capacity and up to 7000 recharges, no other cells come close.

For an e-bike, one of the most essential choices you can make is to purchase the correct battery. For my e-bike, I've had 3 different battery setups. I started with lead acid and quickly found them to be lacking. I carried nearly 50lbs of lead acid with me and even with that they were dead in only 12-13 miles of use. The insane amount of weight meant that when they died before a large climb near my job, I ended up pushing the bike up the hill. Many times I regretted taking my bike when that happened!   Before long you learn quickly that the best batteries for the e-bike (and many other high current applications) are called LiFePo4.  That's the chemical abbreviation for Lithium Iron Phosphate.  Lithium is better than Lead because lithium is the lightest metal.  This particular chemistry is also extremely stable.  Some estimates are that these batteries should last 20 years.  In the lab, they've been cycled over 5000 times before starting to degrade in capacity.  That means they could last 20 times longer than lead acid.

From LIFEPO4

COST

Still, the cost per cell is about 5-8times what you'd pay for lead acid which means you'll be better off financially over time.  I've been able secure a source of these cells from overseas and built up a battery pack that I can use with my bike.  It can handle up to 200amps of discharge, and can give me a > 35 mile range at an average speed of 16mph. At 27mph I get about 22miles out of it.  The pack is encased in Lexan which is very strong and resistance to impact and scratching.  Some say it's bullet proof at the right thickness.  The power supply is included in the case and can recharge after my commute in about 3 hours.

More pictures for those that have an incompatible browser or cannot see the photosynth...