…only got the one light that takes these batteries. The Keepower battery 5500mAh is brand new, delivered last week to replace the Chinese battery.
From memory it didn’t do this behaviour straight out of the box….but my memory is a bit scratchy on that.
You can run the FT03 with a 18650 or 21700. If you have one of those you could use it to see if you still have the problem. It just needs to be a high drain battery.
You say ‘to replace the Chinese battery’, did you order the light with a battery? Does it have a light green wrap on it? If so then they’re not too bad. Try fully charging that one and trying it.
Also, is the keepower one a protected cell?
The one that came with it is a mustard color - 5,000mAh
The 26650 Keepower is same as the one that came with it - button top, not protected - correction, is protected.
Ive charged both and its the same result.
IIRC, there is a threaded ring on the driver side of the ft03? If so, make sure it is tightened down well. Not ridiculous tight but very snug. You can use needle nose pliers in the two notches, If I'm thinking of the correct setup.
If you want to get a replacement driver you can do so via the Mateminco store on AliExpress. You will be looking at $15-20 plus shipping so you’ll need to decide whether it’s worth it
Yes, there is the threaded ring.
You may want to check to see if the temperature is calibrated or at least close. Several of mine were not even remotely close. Now it is one of the first things I do with a new light.
Try the original Chinese battery, it ‘should’ be fit for purpose. If it works properly, the we know it’s a current issue and can advise you on some high discharge batteries that are good. Have you set the temperature setting.
Above he mentioned he tried both batteries with the same result. The SST40 version only draws 6-7A which almost anything could run
It’s not just about size & mAh, the continuous max current it’s rated at is important. Though even a 10A cell should work. Clean the contacts with alcohol, set the thermal regulation to 55°c & try.
I know my Lumintop nano-GT blinks 3 times before it steps down. That light has Nasill, does the FT03 have Anduril?
I sell both variants of the FT03 and there’s no blink, just a hard step down. The FT03 has NarsilM 1.3 and the FT03S has Anduril
Having the temp at factory settings won’t cause a blink either, so it’s not that. A blink is more along the lines of low battery. As mentioned clean contacts, tighten retaining ring, make sure springs are still soldered (had some poorly soldered), check battery is charged with an external charger or DMM.
A video of the issue could be helpful.
Had one customer complain “my FT03 is faulty, can I send it back? It’s stuck in step down” , the next day I get another email saying ” oh, just needed to charge the battery” lol
What are you using to charge the battery? Are you using the built in charger, or a high quality external charger? Do you have a meter to check the voltage? If the charger is overcharging or undercharging the battery it can cause the blinks you describe. If overcharged it can kill a new battery, and undercharged it may just need more charging. I generally do not trust a flashlights charging…also, the USB source might be an issue. From off click the switch fast 3 times for the voltage blink code. Then if possible get a meter to check the battery to see if the onboard voltage is the same as the meter indicates. Once the voltage is below a certain level the light will blink to indicate it needs charging when going to turbo. I am fairly certain the battery voltage supplied is the issue, and if the charging method was the same for both batteries, the results would be the same as well. It does not matter what battery is used if the fault is with the charging method or a faulty charger.
I actually can hardly believe nobody else thought of the possibility of a bad charger or charging circuit in the light. That would be my best guess, because if the issue is with the charging of the battery, it would do the same no matter what battery was used. That would drive someone nuts for sure. If this is the only light you have with a 21700 battery, I would guess you are using the USB-C built into the light to charge it. A lot of chargers will not accomodate the 21700 battery length. If I had to put money on it, I would bet the battery is overcharged or undercharged. The charging circuits on flashlights are notorious for failing to properly charge a battery. Even with my extensive collection of lights, I only have 2 external chargers for 21700 batteries unless you count the olight magnetic charger with magnetic contacts for both sides. I personally usually use the Xtar VC8 for the 21700 batteries. The chances of both batteries being bad is much lower than a faulting charging circuit being used to charge both batteries. There are fairly inexpensive chargers that still work well, but even a fairly expensive flashlight can have a faulty charging circuit, and the Astrolux FT03 SST40-W is far from an expensive light, even though it is a great thrower for the money…one of the best. I would not trust the onboard charging though. I would say get a friend to check it, but I have no friends that have 200+ lights like I do. I just drained a battery on the FT03 SST40-W and it does the three blinks and dims at about 3 volts to prevent damaging the battery.
……I did. “check battery is charged with an external charger or DMM”
Battery that is being used isn’t a 21700 though, it’s a Keeppower 26650 and also the Green 26650 Banggood bundle
That would not matter….I just use 21700 batteries…samsung 40T…because they are were more available and were not re-wraps. My point is the blinks followed by dimming is a low voltage indicator.
I’m aware it wouldn’t matter, but it would have saved you writing a short essay on a 21700 
The circuit on the light does the 3 blinks and dims on the 4th blink when voltage is low…I confirmed that. If the driver is indicating a low battery when a known good battery of sufficient discharge rate is used, the driver for detecting low voltage may be faulty. I use the samsung 21700 with orings as spacers at the top and bottom because I have about 100 of them, and the 30T and 40T are batteries I trust. I suppose it is possible both of your batteries are bad, but not likely. The only thing I can state for a fact is 3 blinks and dimming on the 4th blink is the low voltage indicator for that light model…I have 5 of them. That was actually the light that got me hooked on flashlight collecting…or hoarding. For whatever reason, either the battery is not fully charged, or the PCB is indicating that it is needing charged.
Good one by the way Funtastic, but how do you know how Bart1080 is charging that battery?