Yep, that's how mine work too.
Btw, Im glad I ordered 4 of them - 1 is dead and 1 had a micro-b connector fail (caused by the oaf inserting the cable*). The other two work fine.
*easily fixed as the pads are intact.
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Ah thanks - I'll have to rewire the ikea power connection to USB 
Incidentally 6 hours and still running.
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and a 3 year old cell too !
Yeah I know, just junk!
Btw, I hooked the 18650 board up to my Scope while running a Pi 3B+ and there was no detectable power drop.
Unlike the craptacular "UPS" which had a visible drop switching power sources.
I've now put one into production backing up my C7.
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Oh man, you've really got me thinking about Repeaters and power outage, now.
Can you share some more pic's of the case (assume you 3D printed it) and USB connection as I'm assuming they plug into the wall and stay mains powered but now with battery back up ?
Also with regards to your antenna mod, did you have to cut the trace to the internal antenna ?
With the C7, it runs from MicroB power, as does the Battery backup module.
So all you need is a 2nd USB-MicroB cable to run from the C7's USB Power-Supply to the Battery backup module, then you plug the C7 USB cable into the Battery backup module's USB port and you are done.
Yeah, that's the HE power backed up, which I have via a Talentcell, but I was covering off what I think @rocketwiz is highlighting and that's keeping any repeaters in play, alive during a power outage.
"battery backed ikea repeaters with improved range using an external antenna"
Ah right, my bad. 
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gotcha thinking though now, eh ?
Yep
So I was thinking about what I could use that I already have for Power Failure detection ... and then I thought, what about my WorkShop Pi3B+ Computer? I dont care if it loses power and I already have the "iPhone Wifi presence sensor" devices installed for speedy coming home detection.
So I thought what the heck and added a wifi presence device for the Pi and glued it all together with RM, and hey presto! It works perfectly! 
PS, you'll need an IP device with a Static IP
If you wait a bit I'll have a redesign done as I didn't quite like making the whole thing super long (it was based off the one from thingiverse linked to above), am printing test version now 
Nicely done! I have my pi powered from an SLA UPS and reads the UPS status via NUTS, so when it goes to battery this means mains has failed and this gets reported in node-red and eventually triggers a bunch of shutdown actions when battery starts getting too low.
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Missed this one. There's a j pole antenna on the pcb and just a tiny rectangle of exposed copper you can solder to. Just break the track after this bit and that's it. See here Ikea TRÅDFRI ZigBee signal repeater E1746 inside print cir… | Flickr it's right in the middle of the white PCB.
If you are wanting to do this let me know if you want some tips to take apart the repeater without totally destroying the case or slicing your fingers off 
. I removed both USB connectors as well as the one on the 18650 shield.
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The reason the 18650 board does not drop power is because the output is always connected to the battery, there is no "switch over". This is good for the current range of the Hubitat hubs but might not work will with something the requires over 600 ma continuously.
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BTW, If someone wanted longer up time with their hub they could replace the 18650 with one of theses 18000mAh.
I've only given it a cursory look but in theory it should be just a 1:1 replacement.
Ok here is my redesigned battery backed tradfri repeater. On a 2000mAh battery power outages killing your mesh will hopefully be a thing of the past!
Although perhaps not the best thing to put in your carry on luggage.
The tradfri board is now nicely nestled in its own slot. Please excuse the messy hot glue wire strain relief mechanism.
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Nice work man.
But does it not plug into the mains outlet like a standard Ikea repeater ??
What am I missing ??
The actual repeater unit itself runs off 5V (the other half of the repeater is simply a USB charger).
The micro USB port on the 18650 shield is plugged into the original ikea charger section or any other USB charger with a decent current rating (at least 0.5A for charging the battery, assuming the Banggood specs are correct - most chargers these days will deliver at least 1A) and this supplies power to the shield as well as the repeater. Note that the repeater also has a USB pass though for powering other things. To keep everything as compact as possible I've removed all the USB connectors.
I ordered two of those, and they arrived today. Unfortunately, in my testing, they would not work for hub backup since they appear to briefly cut power when AC power is lost before resorting to battery power. I also had this issue with a different (single-battery) unit I ordered, so I'm not ruling out the possibility that I'm doing something wrong (e..g, what is the "normal" vs. "hold" switch on the side? I can't find any docs, but I've tried it both ways with the same results). I suppose it could also be my batteries, but have several different kinds of reported Sony cells from Battery Junction (who has always been accurate in my experience) and one Titanium Innovations (just wanted to see if a protected cell worked; it fits has far less capacity at the same size, presumably to compensate).
Anyone have any ideas what I might be doing wrong? I have yet another (also single-battery) unit arriving soon in case there was something odd with the specific one I ordered above. If that also doesn't work, I'll become even more suspicious than I already am about what I might be doing wrong. 
Regardless, I suppose these would still work well for repeaters like an Xbee, Dome Extender, or Trådfri repeater--something that won't care about brief interruptions. Unfortunately, at least the latter option above was too much for my hub (haven't tested the two-battery thing yet, but it appears to behave the same based on my USB voltage tester).
Actually it's in the description when you scroll down the product page that you linked to. Can't copy the text (it's part of an image) I'm afraid.
An RC circuit at the 5V terminal would probably solve this (the size of the capacitor would depend on the delay in switching sources (would need a scope for this).
