Rebuilding a Roomba Battery for Less

[New Roomba In Town]

I've been wondering whether it would be economical to just rebuild the battery pack, versus buying a new one. From the looks of it, all it takes is 12 NiMH cells, and from the looks of the case, it looks to be C-Size form factor. For less than $36, I can pick up 12 4500 mAh C cells. I can see iRobot has tried to prevent people from doing this by using TRIANGLE bits for their battery cases, but that's simple to get through.

I'm just curious to find out if anyone has tried it yet, and if so, how it worked out?

If not, I plan on doing this, and will keep you all posted.

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Edit by RoombaReview
I have posted the pictures to the site. They are located at the following URL:

http://www.robotreviews.com/hack/battery.shtml

Craig

[Techfan]

Interesting idea.
Hhmmmm....

[NewRoombaInTown]

Well, I found what I guessed. 12 C-Cell batteries (without the posts), which is exactly what I was thinking of buying for my retrofit of the original battery. I took a bunch of photos of the teardown process. Any suggestions on where (or whether) I should post these? Doing this now proves that it is less expensive to rebuild than to buy new.

FYI - Using a Craftsman Drill with a small flathead screwdriver takes the triangle head screws out of the battery case with very little effort. Taking the lid off is a little more effort as it is a snap on type lid. Use a small flat head screwdriver to pry it open, and then slide across, and Viola... batteries.

[Guest]

Well, I found what I guessed. 12 C-Cell batteries (without the posts), which is exactly what I was thinking of buying for my retrofit of the original battery. I took a bunch of photos of the teardown process. Any suggestions on where (or whether) I should post these? Doing this now proves that it is less expensive to rebuild than to buy new.

FYI - Using a Craftsman Drill with a small flathead screwdriver takes the triangle head screws out of the battery case with very little effort. Taking the lid off is a little more effort as it is a snap on type lid. Use a small flat head screwdriver to pry it open, and then slide across, and Viola... batteries.

Where can one get these C-Cell batteries (without the posts)?

[NewRoombaInTown.]

Take a look at batteryspace.com They have C cells and cells slightly smaller than C. I would suggest going for the ones slightly smaller than the C-cell size only to make sure you can package things nicely. They are 3000 mAh + batteries.

[jonvall]

Sounds like a too much trouble to save so little!

[User]

Doesn't sound like too little savings to me. The batteries being sold around the net are ~$60, not including shipping. I think I might do this just to boost operating time on my Roomba, and for half the price, I'd be willing to spend the 15 minutes to do it.

[robotreviews]

Well, I found what I guessed. 12 C-Cell batteries (without the posts), which is exactly what I was thinking of buying for my retrofit of the original battery. I took a bunch of photos of the teardown process. Any suggestions on where (or whether) I should post these?

If anyone is interested in seeing the pics (I know I am!) I'd be happy to host them on the site. We could also add them into the first message in this thread.

NewRoombaInTown, if you'd like, you can e-mail them to webmaster - at - robotreviews.com

Craig

[jonvall]

Doesn't sound like too little savings to me. The batteries being sold around the net are ~$60, not including shipping. I think I might do this just to boost operating time on my Roomba, and for half the price, I'd be willing to spend the 15 minutes to do it.

Well....to go through that kind of trouble to save $15.00 seems too much for me. A battery for the Roomba Discovery is $49.99 plus shipping and the batteries from batteryspace.com are "less than $36.00" plus shipping.
All I was saying was that it doesn't seem like a great savings to me.

[NewRoombaInTown]

Doesn't sound like too little savings to me. The batteries being sold around the net are ~$60, not including shipping. I think I might do this just to boost operating time on my Roomba, and for half the price, I'd be willing to spend the 15 minutes to do it.

Well....to go through that kind of trouble to save $15.00 seems too much for me. A battery for the Roomba Discovery is $49.99 plus shipping and the batteries from batteryspace.com are "less than $36.00" plus shipping.
All I was saying was that it doesn't seem like a great savings to me.

Perhaps you would feel differently if your intent was to extend the life of the battery for larger operating times? That's the goal here. To do it for less than the battery offerred by iRobot for the Roombas is a bonus.

[jonvall]

Perhaps you would feel differently if your intent was to extend the life of the battery for larger operating times?

You are correct sir!

[NewRoombaInTown]

Well, I found what I guessed. 12 C-Cell batteries (without the posts), which is exactly what I was thinking of buying for my retrofit of the original battery. I took a bunch of photos of the teardown process. Any suggestions on where (or whether) I should post these? Doing this now proves that it is less expensive to rebuild than to buy new.

***Update***

Well, having sent the photos, I anticipate seeing them online for all to see. As for my project, here's where it stands right now... while there are several options, including going to D Cell 9000 mAh batteries (which could triple the runtime of the batteries when compared to the Roomba battery pack), packaging requirements of the Roomba's main customer (my spouse), said that it shouldn't look any different than the original. Therefore, it will be the Sub-C size factor at 3300 mAh.

For those of you that may be interested, the reason behind my even thinking about doing this is that my Roomba Original was acting strange after 1 year's use. It would charge, power up, start the spinning brushes, and then when the wheels would kick in to start the popular circular motion, the robot would stop. Having a new Roomba Red, and slapping the battery pack from IT into the old Roomba, magically everything was fine.

My investigation showed me that the second battery (from the Positive Post) was dead. Every other battery in the pack measures approximately 1.2V. So apparently 13.2 Volts doesn't cut it for the Roomba.

This battery issue I found on my Original Roomba may answer a lot of peoples strange experiences with Roomba Robots. It could be as simple as a bad cell in one of the batteries in the 'pack.'

[robotreviews]

Yes, I received the photos and will be putting them up on Wednesday Evening. (I'm currently on the road and don't have access to post them until then.)

I'm can't wait to see how this experiment turns out. Not only could it be very helpful for those with an original Roomba battery that may have died, but I would love to see a Roomba that can run for 4 or more hours on a single charge as well!

Craig

[robotreviews]

The pictures have been posted to the following page:

http://www.robotreviews.com/hack/battery.shtml

I'll clean up the page and make it a bit easier to load for dial-up users in the next couple of days.

Thanks again NewRoombInTown. Keep us updated!

Craig

[NewRoombaInTown]

Well, it worked. First thing to note, I purchased two sub-C 7.2 Volt Battery Packs - due to convenience and cost. The batteries cost a total of $21. 3000 mAh ratings for each cell on the pack was the size used. Very little soldering later, I repackaged the batteries, original terminals, original PTC, and original varistor. I tested for continuity of each wire to make sure all was right before sealing the case. I installed it into my Original Roomba, and it powered up fine. The battery pack even had enough juice to go for a 2 minute spin. It's charging right now, so I will keep you all posted.

As an FYI - when I originally took apart the battery, the terminals on the PTC looked like they were touching. This renders a PTC useless. When I repacked the battery, I made sure that it was isolated now. I can't say for sure that the PTC issue was the reason for the reduced lifetime of the original battery, but I'm surprised that it was released out of the battery assembly plant with that design.

[Gordon]

NRinT:
Thank you very much for all the reporting. At least two others (roombacommunity) have gone this re-build route, but neither provided adequate information so others could envision the entire process. One source of NiMH cells had been given (www.amondotech.com), but their pricing can't compete with your source. Would you be kind enough to post the URL for your pack-supplier? Or mail to me at gsplewsATverizon.net.

On the "PTC":
1) I too noticed, in your pix, the almost shorted condition and wondered about that as a problem!
2) I would say the thermistor has the NTC chemistry. Here are some data which I acquired on two of my batts:
-----------------------------
The next day (040531), with ambient (and batt-) temps of about
69-degF, or 21 degC:
SERNO 082503's sensor resistance was 11.74 k-ohm. While...
SERNO 022003's sensor resistance was 11.72 k-ohm.

A few days later, attempts were made to measure thermistor resistance
as soon as the Rapid-Charger's LED went OFF; the data are:
3.58 k ohms following charging of #082503, and
3.30 k ohms following charging of #022003 both on 040604.
Data from #022003 was captured without much delay after charge
completion, whereas the #082503 batt had cooled more before
measurement.

3.23 k ohms following charging of #022003, on 040611.
-----------------------------
So you see resistance decreases with increasing temperature.

Once again, thanks for your pathfinding efforts; I know *someday* I will be breaking the case open to re-pack it! One thing I intend to do is drill 2-mm dia. holes, both through the Cover and the Case's bottom, on 2X6 grids roughly in alignment with the cell's axes. When a battery shows degradation, I can begin to load-probe each cell to learn whether one cell is causing the problem.

Regards;
---Gordon

[NewRoombaInTown]

Current Status:
I came back from work, and my Roomba runs like new. It's not as sluggish as it once had been. So, I can now say that this has been a success. And having done it my way, I can be assured of the fact that the next battery I use on my Roomba will not have a "Original Roomba Manufactured Defect" (The PTC issue posted above).

I have sent the photos of the battery packs installed in the case (prior to soldering the original components to the new pack, sealing the case, etc), just to give you an idea of the packaging. Let me know if you have any other questions.

As for the link:

http://stores.ebay.com/All-Batteries-Ou ... ayZ2QQtZkm

You see, I noticed on Batteryspace.com that they sell on eBay. Having found that, I found that they sell the packs just the way we need them. Furthermore, their eBay prices are less than their site. They typically list them on eBay as: Two 7.2V 3000mAh Side/Side Battery Traxxas RC Car New
$21.99. Sorry about missing the additional $.99 in my previous post.

On the subject of longer run-times:
If there's anyone out there willing to double up the capacity, you could get 4 of these packs, and run the second pair in parallel. A slight modification to the top of the roomba would be necessary, REMEMBER you will need to treat these separately for charging, and depending on where you splice, you may need an additional varistor. Needless to say, all of this is done at your own risk. Happy Hacking!

[robotreviews]

Nice job!

The new pics have been posted to the page listed at the top of this thread.

What kind of runtimes are you getting now?

Regards,
Craig

[NewRoombaInTown]

What kind of runtimes are you getting now?

After running it on the first day, I would say I got about 2.5 hours of runtime on the first charge. It's definitely better than the original I had.

[Buzz Lightyear]

Wow! Was that carpet or bare floor?

Buzz