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SRM Dura Ace Battery Replacement at Home Made Easy

Home » Equipment » SRM Dura Ace Battery Replacement at Home Made Easy

I knew this was bound to happen. One day, it simply didn’t wake up. After months of trusty service my SRM Dura Ace Powermeter did not connect to my bike computer.

I bought the SRM second hand, it was fully functional, however, I can tell it has been used a lot. Maintenance history unknown, I was anticipating how on that really important time trial I would lose power data.

Well it was less dramatic than that, one autumn day it simply took 15min till the SRM paired up and the next day I got no response at all. Couple of rides before that I would notice the 3s average power acting weird ( dropping to 100-150W when I was doing a steady 220W average) on some occasions. That should have rang a bell that I need to look into changing the batteries.

Being the DIY type and training with power junkie I set up on replacing the batteries ASAP!

SRM Batteries

SRMs come with two types of batteries – a round lithium cell (mostly older wired units) or 1-2 square 3.6V lithium thionyl batteries. These batteries have extremely low rate of discharge so can be stored for 10 or so years. On one of those lazy weekends I should have opened up my powermeter to see which type it required so when the time came I wouldn’t have to lose a week of having no power data. I always learn the hard way…

My wireless SRM Dura Ace requires 2xLTC-7PN-S4 batteries. The LTC-7PN-S2 is the exactly same unit, however, the wiring terminals are longer and not straight. You can cut and bend them yourself so either type works fine.

In Europe you can find them here under Lithium Primary cells.

In the US here (or Google: LTC-7PN-S4)

DIY SRM Battery Change

Remove the crankset from the bike; unbolt the chainnrings (the small ring holds the plastic cover down)

SRM Dura Ace Battery replacement step 1

With a small screwdriver pry the plastic lid open (there are small indentations at each corner.) start with one side and gently go around.SRM Dura Ace Battery replacement step 2

Carefully lift the plastic lid (some SRM units have wires connected to the lid, DON’T break them!). In my case the lid is not connected to anything so it comes right off. Vóila you see the  two yellow batteries. Notice how the wires are pressed against the walls of the SRM. That is why they need the black plastic sleeves.SRM Dura Ace Battery replacement step 3

Slide off the plastic sleeves of the wires; Using a soldering iron disconnect and remove the old units

SRM Dura Ace Battery replacement step 4

Adjust (cut/bend) the terminals on your new batteries to match the old ones.SRM Dura Ace Battery replacement step 5

Re-solder (RED is “+”; BLACK is ground) and slide the plastic sleeves back over the wires. This one was actually tricky since the terminals need to bent towards each other so that they are not touching the walls of the SRM. I couldn’t get the plastic sleeves back on, however, there is about 1-2mm gap between the solder joint and the metal frame. The black plastic cap holds the batteries down so they shouldn’t be moving back and forth. If it ain’t broken don’t fix it.SRM Dura Ace Battery replacement step 6

If you have a small magnet at hand you can “wake-up” the powermeter and see if it can be paired to your computer. Simply move the magnet back and forth the two long blue components.

Follow the first steps in reverse order to re-assemble the crankset. Wipe off any dust/road grit from the rubber O-rings (and add some silicon grease) to ensure that no water can get inside your precious powermeter.

Re-check if the slope is what it used to be (in my case 18.0Hz/Nm). The zero offset value was around 630-650 before the battery change. It was 555 immediately afterwards. I check it before every ride and will report if anything changes over time. UPDATE: After my first ride I checked the zero offset a couple of times (Garmin Edge 500 updates it as well). It started at 559 and finished at 628, so overall the SRM is back to it’s pre-battery change state.

Re-install the crankset and go ride!

Total time was about 1h, since it has been a while that I have used a soldering iron and also getting the battery terminals bent the right sway took some fiddling. It is a tight space packed with (sensitive) electronics so I was overly careful not to break anything or tear any wires.

It was quite easy to do, just remember to take your time or you risk damaging a very expensive unit.

Good luck!

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Home » Equipment » SRM Dura Ace Battery Replacement at Home Made Easy

14 replies on “SRM Dura Ace Battery Replacement at Home Made Easy”

Brave endeavor! I was so far a little pussy to open up the pandora’s box called the SRM, especially if I think to the many media reports showing, how they actually seal the plastic lid in some kind of oven at their factory.
As you posted this some months ago, I would like to ask you if your DYI has proven a lasting process? to be more precise did you experience problems with waterproofness during rainy/snowy rides? did you find any glue under the plastic lid as you disassembled it? would you recommend the use of some glue or silicone as you reassemble it?

my SRMs are still running, but I expect them to go blank in the near future so any experience is priceless (thinking at the price of €175 and processing time of 30d+ )

In other context did you consider calibrating the device? I made the experience that changing chainrings might actually affect the slope, although it shouldn’t…

Hello and thanks for your comment.
So far the DIY battery change has been successful. I had a bad solder joint on one of the wires that connect the batteries to the circuit boards, however, i think this has been done at the factory and it gave me trouble (no power reading) months after i opened it up. In any case it was an easy fix as well.

Besides some light oil on the rubber seals and the old batteries, there was no glue of any sort on the lid of my SRM. I used regular grease to refresh the waterproofing on the rubber gaskets.

Since i got my SRM second hand, i should have checked the calibration as soon as i got it, however, i rode it for one season as it was. I checked the slope myself 3-4months after i changed the batteries just to have peace of mind and even when using the Ultegra 6700 chainrings the slope was spot on! (I used a 20kg kettlebell that i borrowed from the local gym and i had the nice people at the post office weigh it on their scale; it was actually 19.75kg!) Originally my unit came with the Dura Ace 7800 chainrings. A thread on the Weight Weenies discussion boards also covered chainring change and unless you are switching to ‘solid’ chainrings you shouldn’t need to recalibrate it. I run 54/42 Dura Ace 7800 chainrings for TTs and Ultegra 6700/Dura Ace 7900 for everything else (training/racing, etc.) and the SRM has been performing flawlessly.

I think a SRM DIY battery change and a home calibration(check) with a kettlebell or other known weight is not a complicated task. Of course be careful and take your time. =)

Good luck with all your cycling endeavors!

-Nikola

hi Nikola, thanks for this amazing post! I’m from Chile and it’s real pain in the ass sending the SRM back to the US.
so I bought 2 batteries and will follow your instructions but the calibration thing came up to my mind. will it work flawlessly if I open it by myself?
best,

Hi Pascal,

Thanks for the comment. Changing the batteries does not affect the calibration. As long as you take your time and not rush, you will do fine. A nice feature of SRMs is that you can calibrate/check the calibration yourself by hanging a known weight (±20kg) off the pedals. You can google ‘SRM calibration at home’ for more info. For my own piece of mind, I’ve done it with a borrowed kettle bell that I had weighed at the post office. Calibration was spot on with the factory numbers. Rest assured though that the consensus is that SRMs keep their calibration quite well over time.

Good luck and let me know if you have other questions.

-Nikola

Hi there i have some updates on the battery replacement how do i post them .
I have a 2012 dura ace.and the process is slighly different.
First no need to remove chain rings.
Second there are five small allen key bolts on the back that need to be undone.
Third slowly prive off back plate.
Forth no connection wires but beware not to loose the inner and outer large o rings.
Fith the batteries can be unplugged via small white connection blocks.
Best place to get new batteries OSI batteries.16 bucks each.
Have photos if needed.

Hi Richard,

Thanks for the comment. SRM has gone through a number of (small) design changes as you point out. Feel free to post some pics right into the comments; Wwordpress has such fucntionality. It would be helpful for others undertaking the battery change.

Best,
Nikola

anyone have experience with the SRM-cannondale setup. evidently it has less battery power… I have to return to SRM at least once per year. it is a 2010 model with different batteries than the dura-ace
..

Older SRMs had one round battery, rather than the 2 flat ones pictured here. I assume the Cannondale ones use the single battery setup, hence the lower battery life. I have no actual experience to verify though.

-Nikola

Nikola, thank you very much for this useful article!
tell me please, does SRM have any internal memory? how long can the system be without batteries?

if the system has 2 batteries, I should:
1) remove one old battery, then put one new one, then remove the second old battery and put the second new battery?
or: 2)immediately remove both old batteries, then put two new batteries right away?

Thank you for attention!

Hi Ivan,

Thank you for the kind words. I am not sure the SRM has internal memory or at least the volatile type (one that gets erased if no power is present). Though don’t quote me on that.=)

I have had a SRM with ‘dead’ batteries for at least a week and the slope did not change, though batteries still had some charge, though not enough for the unit to function.

It’s been a while since I had to change SRM batteries, though when i did it, i changed/soldered them one at a time as far as I remember. In any case the slope (calibration) did not change on the few times I changed the batteries myself and I never really paid attention to ‘keeping power’ to the components.

Therefore in my opinion, this is not something you have to worry about. Just take the necessary precautios as when working with precision electronics and you should be fine.

Have fun with the SRM and good luck.

-Nikola

I have just acquired a wired SRM unit, that i need to replace the batteries on, would this be the same process do you know? I am just waiting on the seller to hand over the power control unit, and then i will be looking at doing this.

Hi John,

SRM units have definitely undergone some changes throughout the lifetime of the products, though I would think battery layout would be similar. I have no experience with wired SRMs though this link here should help (http://sprinterdellacasa.blogspot.com/2010/10/how-to-wired-srm-powermeter-battery.html). Just be careful not to rip out any wires and/or take pictures so you put things back the same way. Also there is a Google group called ‘Wattage’ (https://groups.google.com/forum/#!forum/wattage) where people discuss all things powermeter related (training, hardware, etc) so you might find some insight there as well.

Good luck and enjoy your SRM!

Best,

-Nikola

Hi Nikola, i have a SRM ( mtb version ) PM6, but y dont have form to follow your instructions, do you have email to send some pictures?

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