Varta 18682 reflector flashlight dead battery to 18650

[Johniee]

Hello guys!

I got a  Varta 18682 reflector flashlight Link without charger.
The Lead-acid battery was totally dead and heavy, so I want to upgrade the whole thing to 4 or 6pcs 18650 cells.
The original PCB is burnt, the LED is working, it needs 7-800mA.



I've ordered a 10A 1S BMS module for the cells from Aliexpress.
What do you think, which option is better to charge the parallel 18650 cells?
4,2V 5A Lithium charger from Aliexpress or XL4015 DC CC CV Lithium Battery Step down Charging Board with my 12V 4A power supply?

I appreciate any smart ideas

[Swainster]

Perhaps use a USB C power bank control board? That way you could add some extra functionality to your flashlight, although I guess that the overall charge time will be longer.

You can get some pointers from this Great Scott! video: https://youtu.be/yEbbhTw0kno

[tunk]

Li-ion cells should be charged with CC/CV/cutoff.
An XL4015 DC CC CV won't do cut off. Member HKJ has tested 3-4 2S
chargers, none of them does cut-off, most also overcharge the cells:
https://lygte-info.dk/info/indexBatteriesAndChargers%20UK.html
I think I would use slower charging with a TP4056 module.

[thm_w]

Life will be easier if you parallel them as 1S and use a TP4056 USBC module as recommended by tunk.
The only issue is the long charge time, around 1.2A. So if you have 4x 3Ah cells, would take about 12hrs to charge.

There is also the TP5100 module: https://www.aliexpress.us/item/3256804151444891.html
For 1S or 2S. Would handle 12V input. Or maybe the powerbank board mentioned above (if they sell just the board), although I don't have experience with those.

[Johniee]

Thank you guys!
I've ordered the PowerBank module which is from Great Scott recommended!
I also have a PCB board module with 5V 2A charging, this one https://www.aliexpress.com/item/1005004118389586.html

I also was thinking about more TP4056 modules, for each 18650 cells 1 of them

[Johniee]

I've made a schematic for this project.
Do you agree is this a good conception or should I use a plus 3pin rocker switch at the grey(-) output from the PowerBank module?
Then I could choose between the charging vs LED is working modes?
or could it charge the batteries and turn on the LED light at the same time? Can I use this way?
There is that red original switch to turn ON/OFF the LED light 
The LED needs the 1S battery voltage

[thm_w]

You want the switch on the positive power input to your LED driver, after the battery. So what you've drawn looks right.

Some lights prevent turning them on during charging, but, I see no reason why that matters here.

[abdulbadii]

what original PCB function, schematic ?
Imho get such bumped + pole Li-ions along with their quality charger eg. NITECORE New i4, Xtar etc, which'd estimate their capacity

Imho this kind charger is not linear, can do constant current, that is when all clear open DCV MM probe will read 0/low V while a Li-ion being charged will read a V slightly above currently its V 

[Johniee]

Hi everybody!
Thanks for the previous helps! I've made the Flashlight ready to go
4pcs 18650 cells installed inside with the PowerBank module.
It works well with a AMC7135 LED driver on 700mA with the 1S battery cells.
+ installed and hot glued battery level indicator 
As you can see, the result at the back not beautiful at all

Do you think could I fill the gaps nicely around the USB plugs with inserted Dust plugs and with hot glue stick(s) + a kind of masking??
Or what should I do? This is not rain proof this way  I didn't find similar successful project on Youtube with hot glue .

[thm_w]

Ideally you'd start by just cutting out the area you need, but thats hard without a milling machine.

Black RTV silicone could work.
Black hot glue would fill up the gaps as well if you just want it to look better.

But it the silicone won't be waterproof unless you pour a bunch on the inside to seal the backs of the connectors.