Replacing an SRM battery... at home :o)

Discuss light weight issues concerning road bikes & parts.
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mcknightp
Posts: 13
Joined: Thu Jun 18, 2009 7:00 am
Location: Mosman, NSW. Australia

by mcknightp

Hi, here's a link to the replacement guide I put together. They are a custom battery pack & you can't buy them off the shelf anywhere. However, you can buy the batteries from me. I had some made to the same spec as the originals from SRM. Email me off-list.

http://www.swerve.net.au/Images/webguide/

mcknight@bigpond.net.au

Cheers, Phil

wetpaint
Posts: 82
Joined: Sat Feb 06, 2010 2:55 am
Location: USA

by wetpaint

Thanks for this thread :thumbup: I was able to replace the battery in my wireless specialized SRM. The Specialized one uses a Keeper LTC-7PN-S4 battery that I got from http://www.the-powersource.com/keeper2.html. It was quite easy to do, I've done quite a bit of soldering from my days of racing RC cars, but it was really easy to solder a new battery in.

It turns out that the positive wire came loose from the battery in mine, but since it had 400 hours or so on it already and I had a new one I figured why not replace it while I had it open

Here's what the Specialized SRM looks like inside
Image

by Weenie


petal666
Posts: 864
Joined: Fri Dec 12, 2008 5:19 am
Location: Brisbane, Oz
Contact:

by petal666

It would have been much nicer to work on if it was clean. :)

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ms6073
Posts: 2372
Joined: Fri Jul 23, 2004 8:24 pm
Location: Houston, Texas

by ms6073

coloclimber wrote:There are two rectangular shaped batteries in the SRAM SRM wired.
3.5v 750 mAH
LTC-7PN-S4


Bringing this back to the top because after swapping out the SRM bottom bracket magnet mount for a rare earth magnet taped to the frame, it has apparently drained the batteries in the SRM. Over the weekend I removed the plastic torque ring cover and was not surprised to find the wire leads off the plastic cover were a bit short. I checked the batteries with a DVM and although they both read ~3.5v, getting the measurements was a bit problematic as the test leads were hindered by the plastic cover. For those that have replaced the battery in their SRM powermeter, did you remove the torx screws and spindle in order to move the plastic cover out of harms way or simply move the batteries out to the full length of the battery leads?
Michael - The Anaerobic Threshold is neither...

Squint
Posts: 240
Joined: Mon Oct 10, 2005 9:23 pm

by Squint

I always used Torx bits on an extension and a ratchet to loosen the bolts. Then I used the same bits and extension with a torque wrench to reassemble. I've never been able to work with the white disc in the way.

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ms6073
Posts: 2372
Joined: Fri Jul 23, 2004 8:24 pm
Location: Houston, Texas

by ms6073

Thanks for the reply. Was hoping to avoid removing the spindle so as not to have to recalibrate. Can anyone share there voltage readings for brand new rectangluar batteries versus ones that have gone flat? I measured mine the other day and got on average 3.5 volts which is what I thought was the specified voltage or should it be higher?
Last edited by ms6073 on Mon Jan 03, 2011 11:34 pm, edited 2 times in total.
Michael - The Anaerobic Threshold is neither...

Squint
Posts: 240
Joined: Mon Oct 10, 2005 9:23 pm

by Squint

3.5V sounds low. I think the round Electrochem were always at least 3.6V even in the replaced batteries. The discharge curve is pretty flat so it's hard to tell where a battery is at. The best indicator is my experience is ZO instability, particularly when it's colder. I always got wacky numbers long before I noticed the voltage was low. In fact, I have to keep the old batteries separate from the new ones because I can't necessarily distinguish old from new using a multimeter and I don't want to reinstall an old battery.

Image

mcknightp
Posts: 13
Joined: Thu Jun 18, 2009 7:00 am
Location: Mosman, NSW. Australia

by mcknightp

With the new style rectangular batteries, I put a resistive load across the output to generate a current flow of 100mA. Open circuit voltage went from 3.6v to <2v with this load. You can only tell if one of these batteries is dead by measuring its output voltage with a load.

Phil

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ms6073
Posts: 2372
Joined: Fri Jul 23, 2004 8:24 pm
Location: Houston, Texas

by ms6073

Thanks for the additional information. Turns out the batteries were low as replacement resolved the problem. Of course along with the fix came a lesson learned - really powerful rare earth magnets if taped/glued to the frame apparently have the nasty tendency to not let the powermeter 'sleep' which is was drained the batteries on my first powermeter. When I got the replacement batteries, I changed out the old ones for new and promptly reinstalled the SRM bottom bracket magnet mount but since it was covered by black duct tape, failed to notice/remove the other magnet. As a result, when I reinstalled the SRM, I was getting super high power and cadence numbers. :doh: Thinking I had screwed up during the battery swap, I packed up the powermeter and shipped it off to SRM and put the SRM from my TT bike on the road bike with the two cadence magnets. Well this morning I was again reminded of the error of my ways as that other powermeter is now non-functional as well. :oops: Well at least I now know how to change the batteries.
Michael - The Anaerobic Threshold is neither...

JWTS
Posts: 24
Joined: Tue Jun 26, 2007 10:44 pm

by JWTS

pritchet74 wrote:So I changed the battery in my Cannondale Si SRM this weekend. Of course I ordered the battery referenced above only to find out when I cracked the SRM open that it was the wrong battery. For the Si SRM the battery is a rectangular one (as shown below) & not the round one used in the Dura-Ace SRM.


So, just a little cautionary tale...

I have an older SRM Cannondale SI. Guess what? It uses a round battery. I guess the moral of the story is that if you have an older SRM, you should probably crack it open quickly just to make sure what battery is in there. The spider is machined for the battery type, so there's no mixing/matching.

Now for the good news: My SRM had the round battery, but didn't come with the lithium cell shown on page one of this thread; it had 2 CR2430 batteries welded together and wrapped, with solder tabs welded to the battery. Keep in mind this is the battery that came in the SRM new. The battery lasted about 500 hours of use, and was also sitting unused in a garage for about 4 years--so I'd say the battery life was pretty reasonable.

The nice thing about this is that if you're in a pinch (as I was when the battery died) you can find these batteries pretty much anywhere. I don't know where to find the battery solder tabs, but I went to one of those local "battery stores", and they, welded the 2 cells together, wrapped them welded the solder tabs, $9.00 out the door. I got it done at this place: http://www.batterydepot.com/?gclid=CPSO ... gwodvm9KIw

These batteries are much more readily available, so maybe this will help someone else who's in a pinch looking for an SRM battery. I did the surgery and it's working great.

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ms6073
Posts: 2372
Joined: Fri Jul 23, 2004 8:24 pm
Location: Houston, Texas

by ms6073

ms6073 wrote:Well this morning I was again reminded of the error of my ways as that other powermeter is now non-functional as well. :oops:


And to followup, the second SRM was actually fine as the issue turned out to be a issue with the latest firmware updarte for my Garmin Edge 500 (2.6) which does not allow the Edge to 'auto-detect/auto-connect' to powermeters configured on different profiles. Confirmed this with an SRM PCVI which connected fine but the Edge 500 would not connect without either powering off/on after switching profiles or un-pairing/re-pairing the SRM after changing to the new bike profile. On the bright side, my first SRM came back within 11-days looking nearly new as SRM USA replaced my already new batteries, installed the double reed cadence switches, and perfomred a factory calibration.
Michael - The Anaerobic Threshold is neither...

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LarsEjaas
Posts: 259
Joined: Sun Jan 21, 2007 10:52 am
Location: Aarhus, Denmark

by LarsEjaas

ms6073 wrote:
ms6073 wrote:Well this morning I was again reminded of the error of my ways as that other powermeter is now non-functional as well. :oops:


And to followup, the second SRM was actually fine as the issue turned out to be a issue with the latest firmware updarte for my Garmin Edge 500 (2.6) which does not allow the Edge to 'auto-detect/auto-connect' to powermeters configured on different profiles. Confirmed this with an SRM PCVI which connected fine but the Edge 500 would not connect without either powering off/on after switching profiles or un-pairing/re-pairing the SRM after changing to the new bike profile. On the bright side, my first SRM came back within 11-days looking nearly new as SRM USA replaced my already new batteries, installed the double reed cadence switches, and perfomred a factory calibration.


Yep - firmware 2.60 is a REAL NO GO if you are a SRM user :(

If you would like to "downgrade" to firmware 2.40 here is a quick guide:
Download the 2.40 firmware from this link: http://www.garmin.com/software/Edge500_240.gcd

Rename the file: GUPDATE.GCD and copy it to the Garmin folder on the Garmin device.
When you restart the Edge 500 after unplugging it from your computer, the update process should begin.
You may need to remove the GUPDATE.GCD file from your Garmin manually after completing
the upgrade.

Please do this when you have some extra time on your hands - the downgrade (or should I say
upgrade?) will delete all current user data (like bike setup, and screens).
So please write down your screen setup, ODO values for distance, etc. for reference before you change the firmware :smartass:

Yehuda
Posts: 8
Joined: Wed Jan 26, 2011 9:17 am

by Yehuda

Hi long time follower of WW but first time poster.

I am planning to change the batteries in my SRM gossamer as I am getting wonky readings and have problems reconnecting if I stop mid ride or recalibrate.
To send it to Germany would cost over $350 and a downtime of prabably 6 weeks (not very impressive service from SRM)

some simple questions

1) is the removal of the black plastic rear the same as the old white back

2) do I just need to remove the small chainring

3) anyone else done this change on a newer SRM and have any guidlines

I plan to fully document the process


cheers

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LarsEjaas
Posts: 259
Joined: Sun Jan 21, 2007 10:52 am
Location: Aarhus, Denmark

by LarsEjaas

Yehuda wrote:Hi long time follower of WW but first time poster.

I am planning to change the batteries in my SRM gossamer as I am getting wonky readings and have problems reconnecting if I stop mid ride or recalibrate.
To send it to Germany would cost over $350 and a downtime of prabably 6 weeks (not very impressive service from SRM)

some simple questions

1) is the removal of the black plastic rear the same as the old white back

2) do I just need to remove the small chainring

3) anyone else done this change on a newer SRM and have any guidlines

I plan to fully document the process


cheers


Hi Yehuda.

I have to be honest - I haven't tried opening my Gossamer SRM yet (it's only a few months old so really no need to :D).

My impression is, that the difference between the white and black cover is just that: The colour.
One could argue that the black covers are more practical (the white ones will look dirty quite fast).

Yes: just remove the small chainring and the plastic cover should be removable. please be extra carefull when you remove the cover. There is 2 wires going from the cover to the powermeter, and it is important you do not damage those! This thread has a picture of these on page 2 by pritchet74 so you can see what I mean.

But from then on it is just a matter of replacing the batteries with a soldering iron (I am almost 100% sure that the Gossamer has 2 batteries installed, probable the square Keeper II LTC-7PN-S4 but please make sure yourself before ordering).

by Weenie


Yehuda
Posts: 8
Joined: Wed Jan 26, 2011 9:17 am

by Yehuda

thanks I have ordered 2 batteries from the UK (sent to my brother who is currently gloating because he just changed his battery on his quark)

I figured the white and the black are them same

just bought a soldering iron and am practicing like crazy

also if i remove the crankshaft do you know the torque specs

thanks

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