# DIY to the rescue: Polar HRM strap battery replacement



## Kickit

Until I get something better, I decided to revive my old Polar HRM that I haven't used in a few years. The trouble was dead battery in the watch. So I went down to the CVS. I ended up buying a two pack of 2032 batteries and it's a good thing I did. After changing out the battery in the watch, the chest strap transmitter was also dead. The trouble is it's the T31 model strap that is sealed up molded in plastic. I figured it's dead already so I might as well take a crack at fixing it. It worked out well so here is what I figured out:

1. Take a razor and cut around the edge of the larger oval surrounding the Polar logo. Cut along one edge (I suppose you could go ahead a cut all the way around). Don't cut the middle else you might damage the circuit board or components.










2. After cutting it open like a clamshell, you'll see a black plastic cover in the front.










3. You'll need to remove the three small screws in the back to remove the cover and expose the battery.










4. Remove the plastic cover and the old battery. Don't lose the gold leads.










5. Replace with a new 2032 battery.










6. Put it all back together. Use some RTV silicone sealer around the cut edges to seal it back up and tape it to hold in place until it drys.










7. Go have a great workout with lower lows and higher highs.

Now back you our regularly scheduled program...

:thumbsup:


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## 99trek5200

Nice job. I may have to do that soon too as my HRM has been doing funky things, particularly when it is cold.


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## DonkeyMan

*Thanks for sharing!!*

I've got one of the 500 series, 510 i believe, that's been out for years now. Just sitting in my drawer collecting dust. I've got nothing to lose with your DIY tip. Thanks again.


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## serpico7

Pics are no longer up, but I cut mine open with a Dremel: thread


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## MR_GRUMPY

Great idea. I've got an old dead one that I kept (I never throw anythig away), that I will try this on. My current one has a year or two left in it.


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## laffeaux

Thanks!! My Polar chest strap died this past summer, and I've been riding without it ever since. I'll give this a try very soon.


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## messyparrot

*Thanks for the thread, the pics are nice and clear!

Nice job!:thumbsup: *


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## Tugboat

Or you could buy one of the CS600s which comes with a user replaceable battery in the WIND Wearlink strap.


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## MR_GRUMPY

This idea is "slightly" cheaper.


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## 99trek5200

I tried to do mine, but to no avail. One thing that was not obvious in the pictures when I first read the above is that both the front and back of the cover must be cut to access the screws and and remove the black cover. I think I scratched the back of the circuit board trying to open just the back.

Oh well. For $31 I found a new one on E-bay and the 2032 battery will fit in my cycle computer.


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## Fredke

Tugboat said:


> Or you could buy one of the CS600s which comes with a user replaceable battery in the WIND Wearlink strap.


They also make a non-WIND wearlink with a user-replaceable battery in case you don't want to spend over $300 on a new HRM. But it's still almost $60.00, so there's merit in knowing how to cut open an older transmitter and replace the $0.50 battery.


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## Bill70J

*The Approach for a T61 Coded Transmitter is Different*

I have a Polar 720i with the T61-CODED transmitter (N2965). I saved this post knowing I would need it some day. 

My transmitter went dead yesterday, so I attempted to do the "clamshell repair' described here. Having just gone through it, I must say the appraoch is slightly different, plus the replacement battery is No. 2354 vs. 2032. 

If anyone is interested and wants to try this with a T61, let me know and I will post pics.


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## murbike

Oh, man. I think I threw my strap away a couple of weeks ago during a cleaning frenzy.
Damn. Should have known someone here would know how to fix it.

Oh well. Live and learn.

Speaking of HRM, does anyone have any experience with the Timex HRMs?


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## cpark

Thanks!


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## Mr Wood

Doesn't Polar send you a new one if you send in your dead one?


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## rbart4506

murbike said:


> Speaking of HRM, does anyone have any experience with the Timex HRMs?


Yes...Did not have success...Lots of crosstalk and erratic readings....Hence the reason I'm using a Polar now...


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## velodog

Mr Wood said:


> Doesn't Polar send you a new one if you send in your dead one?


Yes, if you send a check also!


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## Guest

Great post as it provides the motivation to attempt the fix.....


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## Adam_SF

The same process works for replacing the battery in the cadence sensor too.


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## murbike

rbart4506 said:


> Yes...Did not have success...Lots of crosstalk and erratic readings....Hence the reason I'm using a Polar now...


Thanks, I'll get another Polar. I liked the one I had, so if there is no overriding reason to switch, I won't.


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## foz

Bill70J said:


> I have a Polar 720i with the T61-CODED transmitter (N2965). I saved this post knowing I would need it some day.
> 
> My transmitter went dead yesterday, so I attempted to do the "clamshell repair' described here. Having just gone through it, I must say the appraoch is slightly different, plus the replacement battery is No. 2354 vs. 2032.
> 
> If anyone is interested and wants to try this with a T61, let me know and I will post pics.


Have you still got those pics? My T61 doesn't have much life left, and I want to try and change the battery myself. Any tips before cutting it open would be appreciated!

thanks


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## Kickit

Followup:

The strap only lasted a few weeks before the silicone started to give. So I would recommend putting some heat shrink tubing to hold it together, that way the silicone is just there for sealing. I ended up getting a new Polar HRM so that I could download the data.

Here is the cost breakdown from Polar:

Transmitter replacement:
T31 (with trade-in) $24.95
T31C (with trade-in) $30.95


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## yakobo

Washing the contact points on the strap with warm water and soap does wonders for these straps as body oil builds up and interferes with transmission. Also, on the wearlink model, cleaning the snaps with some alcohol on a Q-tip will often bring it back to life.


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## hhssss

hi. my 720i coded t61 transmitter just died. can you post pics? i'd like to attempt to replace the battery myself ...




Bill70J said:


> I have a Polar 720i with the T61-CODED transmitter (N2965). I saved this post knowing I would need it some day.
> 
> My transmitter went dead yesterday, so I attempted to do the "clamshell repair' described here. Having just gone through it, I must say the appraoch is slightly different, plus the replacement battery is No. 2354 vs. 2032.
> 
> If anyone is interested and wants to try this with a T61, let me know and I will post pics.


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## Saibots

Thank you so much Kickit for your detailed instructions!

I have a Polar T61-CODED transmitter. I used the same method (steps 1-3) as described above to access the circuit board. For the T61, there are two small screws on the circuit board to remove. However, the T61 transmitter has two gold parts of the circuit board which extends partially into the straps. With a flat head screwdriver, you can work it in between the plastic strap and the gold portion of the circuit board to pop out one side of the circuit board. Once that is accomplished, the CR2354 battery should be accessible. Since batteryspecialists.com has them for 5.99 with free shipping, I am ordering the battery from them.


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## jordachebike

*T61-coded transmitter*



Bill70J said:


> I have a Polar 720i with the T61-CODED transmitter (N2965). I saved this post knowing I would need it some day.
> 
> My transmitter went dead yesterday, so I attempted to do the "clamshell repair' described here. Having just gone through it, I must say the appraoch is slightly different, plus the replacement battery is No. 2354 vs. 2032.
> 
> If anyone is interested and wants to try this with a T61, let me know and I will post pics.



I'm interested and want to try this :thumbsup: Also which transmitter should i buy for the polar 720i?


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## HomebrewMTB

jordachebike said:


> I'm interested and want to try this :thumbsup: Also which transmitter should i buy for the polar 720i?


I would go with a coded Wearlink transmitter (just don't get the WIND version which is for the newer CS series). The Wearlink is much more comfortable and has a user replaceable battery. :thumbsup:


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## Bill70J

*My T-61 Died for a Second Time*



Bill70J said:


> I have a Polar 720i with the T61-CODED transmitter (N2965). I saved this post knowing I would need it some day.
> 
> My transmitter went dead yesterday, so I attempted to do the "clamshell repair' described here. Having just gone through it, I must say the appraoch is slightly different, plus the replacement battery is No. 2354 vs. 2032.
> 
> If anyone is interested and wants to try this with a T61, let me know and I will post pics.


So rather than trying a second battery replacement for the T61, I elected to go with the Wearlink+ 31 Coded Transmitter. Unfortunately, I have since discarded the T61 and the battery replacement pics.

My personal experience using the Wearlink+ with the 720i is mixed. It generally works fine for me if I rigidly follow the Care and maintenance instructions, which call for washing after every use and laundering periodically. However I find that it has trouble transmitting if I am wearing more than two layers, especially if one of the layers is a windbreaker. There seems to be no other alternative, short of replacing the 720i, which continues to work fine after five years of use (but with multiple self-done battery replacements).


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## FrancineTheTurtle

Great project! I followed your lead and thought the following may be helpful:
After removing the screws from the back, I was able to pry the battery out from the black case without cutting up the front and then replaced it with a fresh battery. I also used a window and door silicone sealant and wrapped it up tight with blue painters tape until it dried. Also the watch battery is the thinner CR2025 while the belt battery is the thicker 2032 both available at a drug or food store. The batteries are cheap, 2 packss for about $2.50


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## Mr Fix It

*Polar T31 Transmitter battery replacement*

DIY Repair of the Polar T31 HRM transmitter

Knowing that I’m always up for a fix it challenge, last week my wife brought me her dead Polar T31 for repair. Unfortunately I didn’t run across kickit’s article above until after the fact and took a slightly different approach to replace the battery. The entire project including pictures only took a couple of hours. Using heat shrink has the advantage of future battery swaps taking ten minutes or less.

Step 1, Use an exacto knife and very carefully remove the skin in the rectangle around the polar emblem exposing the transmitter coil and molded plastic above the battery compartment.

Step 2, Using the exacto knife carve a “nickel sized, 13/16” or 32cm” circle in the molded plastic over the battery.. Be careful not to cut through on the left side of the battery where the negative contacts are exposed, see photo. Once a groove is cut into the hard plastic use long nose pliers to remove the plastic in small pieces exposing the battery below.

Step 3, Carefully pry the exposed “V” shaped battery contact upward and remove the battery by prying it up and out.

Step 4, Slip the new battery in making sure the polarity is correct ( positive against the circuit board, negative up ), then install plastic shims over the battery to take the place of the molded plastic just removed. Pretty much anything from your plastic recycling tub, cut to size will work here. Secure shims with a small piece of tape so they don’t move around when you slide the heat shrink in place.

Step 5, Slide a piece of 1” x 3.5” heat shrink in place and heat to complete repair. Let cool and enjoy your refurbished Polar T31.

Notes:
One inch heat shrink is available on e-bay, some electronic parts stores like Norvac and Digi-Key.

Good Luck!


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## martinrjensen

*can't change the attery???*

Are you telling me that you couldn't even change the battery in that thing? wow! I must have a later model Polar and the battery needs changing every few months.


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## Mr Fix It

Yes, the T31 transmitter is completely sealed and not designed for battery replacement. Although the battery is supposed to last 2500 hours, Polar would have you send it back for an exchange transmitter. The battery life on this particular model was several years.


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## qaica

Thanks dude. Please note people, my unit is theT31-coded, and it has the logo upside down to the T31. Take note of the orientation of the band to determine where the battery is located. Here's a pic.


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## tsfdr

*problem is the gasket glue seal is thick and likely can't be cut through with a razor*

problem is the gasket glue seal is thick and likely can't be cut through with a razor in the future.

anyway, $17 replacement chest strap free delivery:Search "heart chest strap" in ebay.com

and,

full heart rate monitor set $30 free delivery:
search 'heart rate monitor watch diving watch' in ebay.com

Please reply.


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## radnaitomi

*T61 battery replacement*

Hi, I hope you still read this forum.

I have an almost dead T61, and I'll try and replace the battery in it.
Could you please send me those pics you mentioned?

Thanks



Bill70J said:


> I have a Polar 720i with the T61-CODED transmitter (N2965). I saved this post knowing I would need it some day.
> 
> My transmitter went dead yesterday, so I attempted to do the "clamshell repair' described here. Having just gone through it, I must say the appraoch is slightly different, plus the replacement battery is No. 2354 vs. 2032.
> 
> If anyone is interested and wants to try this with a T61, let me know and I will post pics.


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## Bill70J

Thanks for the question. I am out of town until Sunday. When I get home I will look at my archived files and see if I still have them. Pretty sure I do. Let you know Sunday sometime, one way or the other. I sent you a pm also.


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## Bill70J

*Back In Town*



Bill70J said:


> Thanks for the question. I am out of town until Sunday. When I get home I will look at my archived files and see if I still have them. Pretty sure I do. Let you know Sunday sometime, one way or the other. I sent you a pm also.


I checked my archived images and did not find the Polar Battery Replacement pics. Sorry about that.

About a year ago, I sold my S720i and moved to a Garmin. I had upgraded the transmitter to a T-61 coded before I sold it, and it worked every bit as good as the original transmitter. Turns out I have a used T-61 transmitter and strap left over. If you're interested, pm me and I will mail it to you for the cost of postage. I just checked it out on our LifeCycle and it doesn't transmit, so I suspect the battery is bad.

Let me know.

Regards, Bill


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## radnaitomi

Thanks for checking. No problem, I'll try and replace the battery with the pics of the t31 then.

I'll have the T61 coded, too.

So thanks for the offer, but I'm okay with mine now (unless I kill it when changing the battery, then I'll contact you again! )

Thanks again
Tamás


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