Changing the flat batteries of a dead Dexcom G4 transmitter (Instruction)

...this is a translation made by wayne, on
-thanks for your work-

Changing the batteries in a Dexcom G4 transmitter

Finally after several failed approaches and destroyed transmitters I’ve done it! First, thanks to all who gave me their "dead" transmitters to be used as guinea pigs. But I did not manage it alone. The brilliant idea came from "afterburner" here on the board with whom I had rain mail communication ;-). Thx Pablo and Greetings to Spain!

So the solution in a nutshell is: Just remove the old 2.1mm thick batteries and push new thinner batteries, with the residual material of the old serving as a contact surface.

The implementation is simple, because you have only to grind an opening.

Required tools and materials:

- Dremel-like tool grinding
Amazon link
- Diamond cutting disc (d = 20mm)
Amazon link

- 1/32 inch cutter
Amazon link

- Multimeter
Amazon link
- Magnifying glass
Amazon link

- Needle File
Amazon link

- Epoxy Resin 2-component adhesive (twin syringe)
Amazon link

Feeler gauge (if needed)
Amazon link

- 2x watch batteries Nr.365 or SR1116W (1.55V) (best order now more due to possible short circuit)
Zbattery link

Note: Some pictures below show a completely opened transmitter to illustrate where the ground is and how it is protected - namely the 9-pole black Power Bridge. This is for information only - the transmitter is not opened completely to change the batteries. In the pictures, a paper disk having the same diameter as the diamond wheel is shown, but again, this is for information only!

Step 1:

Install the blade in the Dremel. Start cutting the back end of the transmitter from the center going straight to the edge. Cut through the middle of the old battery. This will make a loud scary grinding sound. See figure 1.1. Take frequent pauses if it gets too hot from the grinding. Now enlarge the slot with the cutting disk slightly oblique upwards and downwards enlarge sufficiently to allow a tight fit for a new 365 battery. Be careful not to grind out all of the old battery material, since the top and bottom of the old battery will provide connections for the new one.

Now look with a magnifying glass in the slot to if old battery material from both poles is still there. If yes, grind away the leftovers from the outer pole (ring) with the blade slightly angled. This may also smooth some of the inner pole. This is not a problem, as long as some of the original battery material remains connected.

Sanding: (Just FYI, as it probably looks inside the loops. DO NOT OPEN a new battery!!!)

Caution: If the outer pole (ring) of the old battery was not removed by your slightly angled blade and a new battery is inserted, this will create a short circuit that will quickly kill the battery. The outer pole can be seen in Figure 1.5 with the arrow pointed to what needs to be removed.

The figures for the next steps show again exactly how the insides should look.

Step 2:

Now do the front end of the transmitter, just like above, i.e., first centrally then looping around the sides. Here, however, when you start grinding, you will hear no grinding sound, cause the front end is only plastic.

When grinding the front side it is important not to go too far off the center to fall. The grey two lugs (see figure 2.4) serve well as limiting markers. So grind on the sides only as far as the shaft of the blade will allow, when the shaft is touching the corner of each side of the lug.

The front and both sides of the slot must be ground further to allow the height to be increased for the new battery. Here follow the same procedure as in step 1. Use the needle file to smooth the remaining battery material.

Use a magnifying glass to check whether there is still excess metal present on the lower surface of the battery slot. If so grind further, as described in Step 1.

Step 3: Install new batteries

From my experience there are two possibilities:

Possibility 1:

Put in both new batteries and set the multimeter at 2000 mV. The meter
should read stable "020". This is okay and you can go on with step 4.

Possibility 2:

With the multimeter set at 2000 mV and the probe tips now on the sensor contacts on the bottom of the transmitter, test both new batteries. Push on the rear battery and see if the meter reads a voltage. If the reading is between 1 and 18 mV, that’s good. If not push the battery in and out and measure again. You may have a little try this several times. If there is still no voltage even after several attempts, maybe possibility 1 applies. Or you have to try this trick which I’ve used- Simply cut out a small circular piece from the 0.1mm blade of a machinists feeler gauge (or any other scrap of thin hardened metal) with a shear, and with superglue fix the center of this piece under pressure to the middle of the (-) battery pole (figure 3.0). Then carefully push this battery back in and recheck the voltage.

Next, push in the front battery, and measure again at the contacts. If it reads "000", there is a short circuit. The battery must then be pushed a little more forward until the multimeter reads 19 mV or higher. The final thing is to determine if the receiver is now communicating with the modified transmitter. On the receiver, select "Start Sensor" and place the transmitter next to the receiver. After a few minutes the radio icon should next to the battery indicator should show "OK" battery status, and the hourglass is displayed. Note, in my experience a "LOW" battery state is completely normal. That is, you may get a warning for low battery, which can be ignored. This message comes every day always at the same time - namely shortly after you have started a new sensor. So a new sensor would not necessarily be started at night

Hint: I usually recommend to glue a metal piece on the (-)pole for both batteries to minimize the risk of a short circuit.

Step 4: Sealing with epoxy resin.

Mix a small mound of adhesive on a piece of cardboard (wear rubber gloves). Use the epoxy to fill the area in and around the slot to makes the transmitter waterproof. Make sure that it seals the protruding battery well. It may be easier to hold the transmitter gently in a pair of pliers and apply the glue with a toothpick or wooden match. Since the fast-setting epoxy cures very quickly, work relatively fast. You can reapply another mix later after the first batch hardens. Let if fully cure over at least 8 hours overnight.

When done, if the transmitter does not fit in the plastic sensor holder, simply file or grind away the offending epoxy locations.

That's it and you now have your G4 transmitter hacked. Another battery replacement is now child's play. Simply grind the epoxy out with the 1/32 inch cutter and cutting disc and carefully pull or push out the old batteries. Insert a new battery, seal and finish as before. I cannot say which brand of 365 batteries will last longest, but according to the datasheet the 365 RENATA has a 40mAh capacity.

Wishing you much success... Joern, at

Update 1: With my latest replacement, i've taped the sides of the batteries with electrical tape.

This is only optional. Don't forget to glue a round metal piece onto the (-) pole of both new batteries.

Update 2: It's also possible for the front battery to insert the original battery type. I've glued a 0.1mm thick metal piece onto the (-) pole and grinded the front area of the front gap a bit wider. The front gap doesn't completely cover the battery, because it's too thick. So, the cell sticks out a little bit. That's no problem - you can seal this very good with epoxy. I've taken a Maxell 391 cell (55mAh). This is the original battery type. I can also recommend the renata 391 (50mAh). This one makes the contact a little bit easier.

Here are two pictures:

You can see that the battery sticks out a little bit through the epoxy ;)

Now my receiver shows me the battery state: OK.

694-Dexcomdisassemblyfigures.pdf (578 KB)
1 Like

Cool info. Thanks for the details and taking the time!

If I send you a dead G4 transmitter, will you replace the batteries? I will pay all shipping ,battery and any other costs.

Good job.
But why change battery, i thought one is supposed to replace the transmitter

This is for the direct payers to save money.

Wow! I don't have the skills or the tools to do this on my own, but this is incredible stuff. Impressive work and thanks for posting the info!

Whoami, it’s not difficult and you can buy all tools online from amazon. Try it out.

I am having trouble understanding the fairly poor automatic Google translation. I have an American friend who has been working in Germany for a few years. I have asked him to try translating it. If he succeeds, I will post it here.

For example, here's the beginning of step one:

Clamp the blade in the Dremel and the transmitter center back to
to the edge (transmitter end) by the internal battery through separate.
It always take a break because of grinding heat. Now the slot
with slightly oblique held blade upwards and downwards enlarge
to the new 365er battery can be pushed tight in half.

I think a human can do better than this. In any case, great work Joern and I look forward to trying it soon. If I mess up, I can get a new transmitter after a 20% copay.

Okay John, if your friend doesn’t have the time, i will make an english tutorial, too.

Actually i've taken a stab at correcting the English in the translation. There are a few things, however that are not clear, either in the google translation or with my limited German. Alter Schwede! It's right now in a word document with the unclear section highlighted. Is there a place i can send this so perhaps you can now correct my English ;-)

You can send it to me and i will translate the unclear section. I send you a pm ...


Great work on this! I saved my dead transmitter with the idea of doing this. I have the materials, could I please get a copy of the English translation that you and Wayne are working on when it is done?


Chris G

I can post it on top of this discussion instead of the link to the german one.

Done! Thx, wayne.

Thanks for doing this. The Amazon link to the epoxy is not right. Goes to a flat diamond needle file.

Thanks Joern and Wayne!

This is great. I am ordering the tools now. Very glad I saved my last transmitter!

I have the tools in hand, too. I am just waiting to have enough time. Please report your success and any issues you may have along the way.

Fixed now

Thanks for the DIY battery change techniques.
Though the G4 Receiver is likely to fail electronically prior to the rechargeable battery going bad, I did find out that the Receiver is much simpler. My Receiver failed after 14 months of use and seemed that my insurance and supplier were going to result in my cost being $480 - final result was my highest copay. 2 weeks after initial request I finally received a new Receiver. Besides all that:
The battery is a 2.05" x 1.26" x 0.21" 970mAh, 3.7V, 3.6Wh made in Indonesia. Numbers on the battery are: 1/LPP 473350 8TH PCM WC and VKB: 56479 201 012. Battery is located behind the display and connected by a simple miniature 3 pin connector. The connector is easy to disconnect and I can only suspect that only severe drops would knock it loose sealed in the case.
I used a very thin cutting blade on my dremel, cutting along the seam being careful not to cut too deep. If you cut more than 0.16" past the main body you may cut the electronics. Once I saw the plastic removed in several locations I used a small flat screwdriver to pry the case apart, cutting any excess plastic still holding it together. There are 3 tiny hex head screws (jeweler’s size?) holding the circuit board in place.

699-G4Rcvrguts.JPG (795 KB)

Freaking genius man. I tried cutting one easy task.