Boosted Rev Battery Teardown (and failure)

 Boosted Rev Battery Replacement - Teardown and and failure READ UPDATES!

For downloads, refer to https://github.com/MichaelCastiau/boosted-rev-battery-replacement

UPDATE: The rebuild of the original battery ended in a complete failure :( Boosted has made it absolutely impossible to even replace the Li-ion cells inside it's battery. Read dedicated article for more information.

About 2 years ago, I bought a Boosted Rev scooter. A powerful, robust, reliable scooter that I use almost daily. Heavy usage, that is. I use it as I commute between home and work, when going for groceries, visiting friends... I am very impressed with the work the engineer team pulled off with this product. It has very smooth acceleration curves, feels very solid and I haven't had a breakdown.... until now.

Over the course of the last year, the battery capacity has reduced drastically. I now have less than half the initial capacity. (Although it's sad to have less capacity, this is expected behaviour of Li-ion cells. Most cells last between 500 - 800 charge cycles. Since I have been using my scooter almost every day for the past year, it makes sense the battery lost much of its capacity.) 

Under normal conditions, I would go and buy an OEM battery from Boosted, that is, if it weren't for the fact that they went out of business. I went searching online for a replacement battery, but it's out of stock in all the warehouses that ship to the EU. I was faced with a choice: buy a new scooter from another manufacturer (which is a pity because my Boosted Rev hasn't let me down and the frame is in very good shape), or try to replace the battery myself. I went for the latter. Here's a step by step overview of how I proceeded.

If you were to follow the same steps to repair your battery, please note that this is entirely at your own risk. I'm by no means a Boosted engineer or salesperson. I'm a software engineer that studies electronic design in my spare time. Opening a Boosted battery is dangerous, irreversible and you should proceed with extreme caution.

My first approach was to check if I could simply build a battery pack and wire the minus and plus to the corresponding terminals, but as I'm sure some of you will have found online, you can't do that. The Boosted Rev ESC (motor control system, some calling it the 'mystery' box), will only accept current from a battery that previously proved itself to be a Boosted OEM part. The battery does this by communicating with the ESC through a CAN bus. (This is why the battery has more terminals than just minus and plus).

So unless I 'mimic' my pack to be an original Boosted Battery, making a custom pack is a dead route. (Note:  https://github.com/rscullin/beambreak did reverse engineer some of the communication between the battery and the ESC. Much of the commands interchanged are still mystery, but it proved to establish a valid communication between a computer faking being a battery and a Boosted ESC. So technically it should be possible to create a fake Boosted battery pack , considering a microcontroller with CAN bus is added in between that implements the reverse engineered code)

The plan is as follows:

• Open the battery pack (being VERY careful not to damage any Li ion cells inside, as they could easily overheat/explode)
• Salvage the internal BMS (the printed circuit board), being careful not to damage it or fry it with static electricity
• 3D Print a new casing
• Fit new Li ion cells and rewire the board (36 cells in total)
• Assemble the new casing with the battery pack, making sure it is watertight

Opening the Boosted Rev Battery

Boosted did a very good job with this battery pack to make it almost impossible to open or replace. If you decide to open up the case, it will NOT COME TOGETHER AGAIN. Also note that replacing the battery became a tedious and expensive process, so proceed at your own risk.

The first step is to remove both caps at the end. Remove the small screws using a micro Torx screwdriver. The caps are glued in place, so you'll have to break them to be able to remove them. Be careful not to damage the connector while removing the caps!

I used  a flat screwdriver fitted in between the edge of the cap and the casing to break the glue. Once the seal is broken, it was actually relatively easy to remove the cap. This of course also means your battery isn't waterproof anymore.

After both caps are off, you'll soon realise that the entire pack is glued inside the case, so you can't just pull it out. (Believe me, I tried) So the next step is using a Dremel along both horizontal edges of the battery to slice the casing in two parts.

PROCEED VERY CAREFULLY! You do not want the Dremel to slice a Li-ion cell open!! The wall thickness of the case is appr. 2mm, so only push the Dremel very slightly in the case. Go slowly and pause your work if the case is getting hot. The metal of the case conducts heat very well, which isn't optimal for the Li-ion cells.

Once the metal case is separated, both parts should come off rather easily, just pull and break the glue.

The Boosted battery with the bottom metal part off. The yellow strip is disconnected from the PCB

Once the metal parts have been removed, you are left with the raw battery pack. Be careful not to destroy these components, because we'll re-use them in our new pack.

The Li-ion cells are fitted in custom plastic/metal holders. All cells are glued in place. The holders are held together by the welds of the cells. So don't try to force open the plastic casing!! The circuit board is very tightly glued to the plastic casing. Don't try to pull the circuit board off, you'll break it.

There is a yellow strip (flexible PCB) that runs across the battery, connecting all the balancing wires. Unfortunately, it is very difficult to remove and salvage that strip due to how it is soldered. Disconnect the strip from the BMS circuit board very carefully; You may have to remove some silicone to access the connector. These are all very fragile parts, so I can't stress enough, go slow and be careful.

In my case, the yellow strip broke, so I had to find a new way to connect the balancing wires. The connector on the PCB is a 20-pin FPC 0.5mm connector. I designed a small custom PCB that can be manufactured and used as a replacement to the yellow strip, so if it does break, there is another option available. (Download design on github).

Balancing Wires (Custom Yellow Flexible PCB)

The yellow strip counts 19 wires. The connector has 20 pins. You'll notice boosted wired the two last pins of the connector together. This is a design that I didn't see the first time I tried to replace it. Boosted most likely used a 20 pin connector because they are more available than a 19 pin one.

19 wires of which:

• 12 balancing wires ( because the pack counts 12 x 3cells, also known as 12S3P). Each balancing wire also inter connects to a fuse.
• 6 wires for temperature sensing (there are 3 10k@25 celsius thermistors embedded)
• GND

The balancing wire of cell 12 is on pin 19 AND pin 20.

Ideally, carefully remove the yellow tape from the top of the strip. Desolder the connections that are made at the edge of the strip, making sure to be quick. The heat from the soldering iron can damage a connected cell (making it possibly burst in flames). Once all the solder connections have been removed, very carefully detach the trip from the pack. It is glued in place, so you may use some alcohol or other solvent to remove the glue.

If it were to break: Just rip off the strip by cutting the connections and throw it away. You'll be using a custom pcb to reconnect the balancing wires to the board.

Disassembling the pack

The battery pack is held together by three 2mm rods that go through the different casings. At the connector end, start by simply unscrewing the plastic part that holds the wires, then remove the 3 small silicone caps, revealing the 2mm rods and bolts. Remove the bolts (and don't lose em). Once removed, the only thing holding the casings together are the welds of the cells.

Before removing the nickel strips, mark the order of the plastic casings. I didn't and it was a tedious task trying to figure out the correct order to re-assemble it.

Cut both the + and - wires connecting the pack to the BMS. You won't be needed these for now.

Don't try to open the casing by itself, it won't work! You need to remove all the welds first. I used pliers to pull the nickel strips of all the cells. Be careful not to accidentally make contact with another cell and shortcutting it when removing the nickel strips.

You may throw away the strips, we'll use some new nickel strips to re-weld the new cells.

Once you start pulling the nickel off, the casings will come apart. You can then remove the cells. The cells are glued in place, but easily come off. Be careful while handling Li ion cells. Once the fitting is empty, clean out any residue and set them aside, remembering the order in which they were fitted.

Removing the BMS is difficult. It very well glued in place. I ended up pulling carefully the BMS up and slowly cutting the glue with a very thin hobby knife. Be very careful not the damage the PCB, you'll need it later on!

I also ended up unscrewing the connector and removing it from the end cap. Desolder the connector wires from the BMS. Take a picture before desoldering so you know where to re-solder the connector later on.

Fitting new Cells

The battery is composed of 36 Li-ion cells of type LG INR18650HG2. At the time of writing, these cells are very difficult to find in the EU due to the current Covid pandemic. I however could order some online. Start fitting the new cells in the casing, respecting the exact order in which they were connected before (refer to the schema). Each 3 cells are connected in parallel. Then, these get connected in series. So in total you have 12 series of 3 cells = > 36 cells.

I used a cheap battery powered welder from Amazon to weld the new cells in place. It is not super powerful, but it does the trick. Start by welding the parallel connections of all the new cells.

Be careful not to shortcut any cells. Also check that the welds hold in place. Continue to weld all four cases. Next, cut 12 nickel strips and solder separate wires to them, these are the balancing wires. Do not weld the series connections and then solder wires onto them. This could make a Li ion cell overheat.

(I decided to double weld the series connections. I didn't find any real information about the current ratings of the battery, but judging they used 11 AWG wire, a connector that is rated for 25A and motors that run 750W each, I suspect the current rating should be somewhere between 20A - 35A. You don't have to double weld, you may for example use thicker nickel, but I wanted to make sure the strips wouldn't overheat.)

Weld the cut nickel strips with the wires in between the cells, connecting them in series. Refer again to the schema. Be very careful to check polarity. When measuring voltages across one casing, each casing should measure around 10V.

You should end up with 12 balancing wires across the whole pack. Let them hang out on the wide part of the casing (top of the battery). Mark the balancing wires to know which is which. I did this with some painter's tape.

Reassembly of the pack

Once welded together, I added some kepton tape in between the separate casings (Be careful not to cover the holes where the rods will come through). This is so that in case a weld comes off, it doesn't short circuit another cell on the adjacent side. Bend the welds so that the four casings line up, balancing wires coming out on the top side of the battery. Then, you should be able to slide back in the rods, and tightening the bolts, the pack should again be assembled, feeling sturdy. If welds come off, now is the time to correct them.

Don't be tempted to solder nickel to the cells, since this could overheat a cell and prove very dangerous.

Measuring voltage across the entire pack, you should see apprx. 43V. This proved correct in my case and overall, I was very happy with the result I got this far.

The yellow strip survived.

If you managed to get the yellow strip off, refit it on the pack and solder the balancing wires to their respective connections. The cells numbers are indicated on the strip. You may use some kepton tape to glue the strip tightly to the pack.

The yellow strip broke.

If you didn't manage to salvage the strip, manufacture the custom pcb. (Download on github.) I usually order my PCBs on JLCPCB, but any other service would too. You also have to order some minor parts. Solder all parts in place, if you didn't choose for factory assembly. The parts are fairly small, but with soldering experience and flux, it shouldn't be too hard to complete.

Fit the custom pcb on the top side (wide part) of the battery pack. Solder the balancing wires to their respective connections (cells markings are on the PCB). You may use Kepton tape to hold the PCB in place

Mounting the BMS

Once previous steps completed, you may remount the BMS on the underside of the PCB (narrow side). Reconnect the yellow strip, or use a flat cable to connect the custom pcb to the BMS. Once the balancing wires are connected, you may re-solder the + and - connections to the pack. Use the screws to hold the BMS in place. Additionally, you may re-use the plastic parts that slide in the holes in the middle of the PCB.

Printing 3D parts (Waterproof!)

I designed custom parts that can be 3D printed to make for a new battery casing. If printed and mounted correctly, the part should fit exactly inside your scooter. I used PETG material to print the casing, since it is very robust, flexible and waterproof, which should help when sliding the battery pack in place. You may use a 3D printing service or your own printer to print the parts. However, the main part is 31 cm high, which most services will bill a lot of money for. You may also contact me if you want me to print the part for you, which for sure will be cheaper than a printing service.

The pack consists of 3 parts: 2 lids (one having a fitting for the battery connector) and a main casing. You will need some 3 mm screws to screw the lids in place.

Slide the battery pack into the casing, being careful not to break any parts. Then (considering you have cut off the connector already), prepare the connector for soldering. Pass the BMS wires through the hole on the front lid. Remove the crimping material on the connector and remove any excess glue. Re-solder the connector wires, using new crimping material to seal off. Then, push the connector through the hole, making sure it is oriented the right way. Some 3mm screws (or the original ones) will hold the connector in place. Use some glue or caulk to optionally seal the connector from the inside. If printed correctly, this connector will be waterproof.

Slide both caps over the main part. Use 3mm screws to screw the lids to the casing.

If you want the casing to be watertight, seal the caps with some caulk when sliding them over the case.

ET VOILA!

Place your battery in your scooter, connect your connector and it should be up and running again! If any problems arise, or you want to replace the cells again after a year or two, it should be easy to re-open the case, or print 3d parts if they break when opening.

UPDATE 1:

Don't cut the wires at the connector, but desolder the wires from the PCB without cutting. I wrote differently in the first version of this post and this forced me to order a new connector (which isnt cheap).

UPDATE 2:

Bad news. Thus far I replaced all the cells and the Boosted BMS just went into complete shutdown mode. It seems that the BMS remembers the values of the previous cells. If they do not match (meaning the cells swapped out), the BMS locks itself. There is no way to get it to work again.

It seems that someone at Boosted did a VERY good job at preventing any kind of repair....

I've also been tinkering with the CAN bus of the boosted battery, and it seems that a special heartbeat should be sent on the BTN line, before the ESC even activates the CAN bus. To be followed.