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

Discuss light weight issues concerning road bikes & parts.
Tug Boat
Posts: 196
Joined: Tue Oct 30, 2007 3:09 pm

by Tug Boat

Well, I moved it from being sandwiched between the frame and cable guide last night. First, I did the little test of running the sensor across the back to make sure the batteries were still working. Then I moved the sensor. Rode it this morning and it works except for when I hammer out of the saddle. I'll play with it some more, but at least it's working. Thanks for the suggestion.


Posts: 1405
Joined: Tue Sep 14, 2010 3:28 pm

by bricky21

Use a penny or a dime to space the sensor from plastic plate. If it's to far or to close it won't transmit the signal properly.

by Weenie

Posts: 3
Joined: Sat Feb 12, 2011 5:35 am

by srhendricks82

So I am currently in the process of replacing the round battery on my 7800, but the replacement battery I ordered has 3 pins...I'm assuming that two of them are negative...does this mean that I should connect the two outside pins to the black wire, or just connect one of them? Here is the battery I have

Posts: 7
Joined: Tue Mar 13, 2007 4:11 pm

by fuzzalow

You need only connect the ground wire to one pin. Snip the other pin off.

Posts: 1701
Joined: Fri Dec 24, 2010 9:37 pm

by sungod

just replaced the batteries in my sram s975 cranks (srm wireless)

it needs two batteries

original type LTC-7PN-S4, but these were out of stock so i used BL-7PN, these are the same except they have two additional cathode pins, these can just be 'peeled' off the end of the case

note that this type of battery can be marked either 3.5V or 3.6, it just depends on the reference conditions used in the specification, don't worry, they're the same really

remove the chainring bolts

remove the small chainring, this reveals the small indents next to each hole

use a small screwdriver, poke it in one of the indents and lever off the cap over the electronics - there are no wires connected to the cap, it can be removed completely

before pic, i've inset a zoomed in view of one of the indents


on each battery terminal, there's a piece of insulating sleeve, carefully slide this down the wires leaving the soldered connection visible

wires.jpg (5.83 KiB) Viewed 3100 times

use a small soldering iron to disconnect the battery, take care not to let the wires spring back as they could flick solder into the rest of the electronics, remove the battery, it's held in place by some mildly tacky stuff

repeat for other battery

trim the terminal leads of the replacement batteries to the same length as the originals and tin them, also re-tin the ends of the wires from the srm

solder the terminals of the new battery

once cooled, slide the insulating sleeves up over the joints

gently bend the cathode wire (-ve) towards the axle - otherwise it will foul on the edge of the housing

push the battery back into place

repeat for other battery

after pic...


if you've got a magnet handy, move it past the two reed switches a few times to wake the srm, it should then be detected by your head unit, you can check the zero offset, it should look like it used to before the old batteries got tired

check that the seals on the cover are in place, line up the white dot so that it's centered on the reed switches and push it back on, the make sure it's fully seated all the way round (if there was *any* sign of water/crud having seeped in, check the seals are ok, put some extra silicone gel on them)

replace chainring, do up chainring bolts to 10Nm

refit to bike, ride

Posts: 135
Joined: Sat Oct 04, 2008 10:09 am

by nutty

having trouble fitting the back cover back, the outer o ring seal seemed to be worn out and occupying the space meant for the back cover to sit in tightly. Any suggestions? Replacing the O ring seal? Does anyone know the exact 'spec' of the outer and inner o ring seal? Do I still put bait of silicon grease on the O ring seal before putting the cover back?


Posts: 35
Joined: Mon Sep 19, 2011 4:37 pm
Location: France

by Carcinogent


I just replaced the TWO square lithium batteries in my wireless Dura Ace 7800 SRM. For the full instructions I made a nice tutorial at my blog: ... made-easy/" onclick=";return false;

I included a link with where you can get the batteries in Europe.

Posts: 1
Joined: Sat Dec 01, 2012 4:20 pm

by andmaraujo


this week failed to record my SRM power and cadence. Believing be the battery, I decided to follow the tutorial brir and replace battery. However open when checked that the wires that connect the plate abteria were loose. The battery is ok but do not know where to solder the wires in the dve circuit board. Could anyone help me with a photo, or indicating which location? My SRM is an FSA K-Force Light. The problem is not that the second battery that has the grounding screw.

Sorry the bad english!!

Posts: 30
Joined: Sat Mar 10, 2012 1:00 pm

by notaero

I think it's time for me to open up my Rotor 3D+ compact SRM and swap the battery. At the moment I'm seeing the unit pair to the PC7 within about 5 crank revolutions, and it shows the correct ZO and slope. It will transmit cadence but will not transmit power. Before I remove the crank set, can anyone suggest if this is indeed behaviour suggesting a flattening battery, or whether something else might be the issue here? It's seen about 400hrs of use so far, which is a little soon for this to happen.

User avatar
Posts: 2603
Joined: Fri Jul 23, 2004 8:24 pm
Location: Houston, Texas

by ms6073

If the SRM 'wakes up', pairs, does not exhibit noticeable drift of the zero-offset, and you get cadence but no power, then it unfortunately does not sound like an issue with the batteries.
Michael - The Anaerobic Threshold is neither...

Posts: 30
Joined: Sat Mar 10, 2012 1:00 pm

by notaero

Hmmm.. On second inspection, I think the ZO may not be 'steady'. depending on the crank arm position I see between 20-30 Hz difference. I popped the cover and everything looks perfect inside. I'm going to replace the batteries and see what happens from there.

Posts: 11
Joined: Sun Jan 08, 2012 7:49 am

by doggatas

Getting a SRM DA 9000 power meter very shortly. My bike has DA 9000 with standard chain rings(53/39), I opted to purchase my SRM with compact chain rings as the one DA 9000 spider accepts both standard and compact chain rings.

I purchased in this configuration as I was going to by compact rings anyway for days in the big mountains and bought the SRM this way as a cost effective way (if you can call it that) of getting the compact chain rings.

98% of the time i will be using the 53/39 and therefore plan on removing the compact rings off the SRM before I even install the SRM and install the standard rings from the DA9000 crank set. After reading the posts in this thread about how the small chain ring seals and keeps the cover in place, is this something I need to be wary of when swapping over the chain rings??? I mean will removing the small chain rings pop the cover (i hope not) or is there something else needed to actually remove the cover?

Posts: 293
Joined: Wed Jun 09, 2010 10:44 am

by WeightySteve

The only thing keeping the cover on once the rings are removed is friction between the internal rubber seal and the spider housing
however, there is enough friction involved so as not to let the cover "pop off" when you remove the rings. Don't worry, changing the rings is just as trivial as changing them on a normal (non SRM) spider.

Posts: 553
Joined: Sun Nov 13, 2011 6:00 am

by DartanianX

Does anyone know how to use the new software function to check the levels of the battery crank?

User avatar
Posts: 3039
Joined: Sat Jan 03, 2009 9:43 pm
Location: Canada

by devinci

DartanianX wrote:Does anyone know how to use the new software function to check the levels of the battery crank?

I was told its when you dld a training file from the PC7, I guess its via the SRMwin software, but not sure. This is an awesome feature though.

by Weenie

Post Reply
  • Similar Topics
    Last post