# DIY to the rescue: Polar HRM strap battery replacement



## Homebrew (Jan 2, 2004)

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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## jakomonster (Jun 20, 2006)

i always wondered what it looked like inside there... nice work.


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## paulrad9 (Sep 29, 2005)

VERY nice, thanks for sharing!


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## WolverineGator (Feb 26, 2004)

*Good info*

Another tutorial on how to replace Polar heart rate monitor chest strap batteries: www.tinyurl.com/wkdb

"Strap Battery Replacement:

I, however, was faced with the task of either caving in to Polar's
outrageous fees for a re-newed strap, or figuring out how to change the
durn battery myself. Using an exacto knife, I carefully removed the
back part of the center of the chest strap. And exposed, to my dismay,
the solder side of a little printed circuit board. But wait! There
were two prominent solder pads visible that seemed to be connected to
the battery on the other side. A quick check with a volt meter
confirmed that this was the battery site, and that my 3 volt lithium
battery was already down to 2 volts. From the position of the pads,
and my knowledge of how solder pad lithium batteries usually are set up,
I could estimate the size of the disk-shaped lithium battery. I then
turned over the strap and, using a dremel tool, gently and carefully cut
into the plastic on the front of the strap in a rectangular pattern
7/8 in. long by 3/4 in. high over what I guessed was the battery.

The battery, a CR-2032 type, was immediately exposed. Looking
around, I also could see the circuit board, with lots of little surface
mount discrete components. Looking more closely, I noticed that about
1/64 inch or less above my top cut there was a one inch long, very fine
cylindrical coil. Had I been the tiniest bit higher in positioning
my cut, I could easily have cut into that coil with Dremel tool drill.

With both the front and back of the battery part of the circuit
board exposed, I desoldered the old battery, and installed short, fine
wires. I then soldered them to a suitably insulated fresh CR-2032
battery, installed the battery, restored the back part of the strap,
taped the front over with duct tape, and then put heat shrink tubing
over the entire mess for a clean, professional appearance. Next time I
need to replace that durn battery, I can quickly cut off the heat shrink
tubing, remove the duct tape, solder in a new battery, and seal the
thing up again in what should be no more than a 5 to 10 minute process."


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## RedBlueGreen (Aug 22, 2007)

WolverineGator, that was excellent! and thanks for sharing your expertise. It'll save people loads of money in the long run. Cheers!


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## mbaulfinger (Aug 2, 2007)

Hi Homebrew and All,

First of all thanks for the information. I've cut and lifted the front plastic portion of my strap and exposed the battery. It looks like the lead on top has to be de-soldered from the circuit board to remove the battery. From what I can tell the bottom is also fastened to the circuit board. Do I need to cut enough of the strap to remove the circuit board in order to get to the fasteners that hold on the bottom of the battery? From the earlier posts, it's implied that you have to expose both sides of the circuit board to get the job done. Also, how does the RTV do holding everything back together and keeping water out (I sweat alot when I ride hard.)? The head shrink sounds like a good idea too. Thanks for any responses.

Regards,
Mark


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## Homebrew (Jan 2, 2004)

mbaulfinger said:


> Hi Homebrew and All,
> 
> First of all thanks for the information. I've cut and lifted the front plastic portion of my strap and exposed the battery. It looks like the lead on top has to be de-soldered from the circuit board to remove the battery. From what I can tell the bottom is also fastened to the circuit board. Do I need to cut enough of the strap to remove the circuit board in order to get to the fasteners that hold on the bottom of the battery? From the earlier posts, it's implied that you have to expose both sides of the circuit board to get the job done. Also, how does the RTV do holding everything back together and keeping water out (I sweat alot when I ride hard.)? The head shrink sounds like a good idea too. Thanks for any responses.
> 
> ...


The battery leads on mine weren't soldered. It was held on by the screws as shown. I had to cut the back side to get to the screws that held the black plastic cover in place as well as held in the battery lead. Yours may be a different model and similar to Marty Goodman's as referenced above.

I've only been using it for two weeks but so far the RTV has held up well. I don't anticipate any troubles.


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## Iowagriz (Jan 14, 2008)

Not sure if my pics will upload or not, but here is my attempt to replace my battery.

Pic #1 - shows what the back looked like after surgery (in an attempt to show what it looked like before). My strap was replaced in 06(?) and the contact patches are rectangular. You can see where I cut around the harder plastic and the softer plastic to remove the back. The triangle cuts were to access what I thought were the screws holding it all together.

Pic #2 - shows the front of the unit.

Pic #3 - is what it looks like with the back removed. Again, I had tried to find the screws to free the circuit board. Don't bother on this model, those "brackets" are the connections from the HRM pads. I ultimately broke them and killed the project.

Pic #4 - shows the guts when removed. On this model, I think that the battery would be very hard to remove even if you could get to it from the front. You can see a small round indent on the strap part. Your only chance is to expose the battery through this spot. I marked the top of the circle at the top of the "L" in Polar on the front side. The bottom was at the bottom of the plastic.

Pic #5 - shows the circular access ident on the strap as describe above. The "L" in the wording is closest to you in this picture.

Again, I don't see how you could get the battery out from this little access point. There is no way to access from the back without breaking the HRM pad leads (IMHO).

Oh well, I figured I wasn't out any money as I don't remember Polar giving me a discount for returning a worn out strap for a replacement.


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