The new flashlight... sat for a year and its battery died (as it turned out, this happens with similar flashlights, the same thing happened to 4 friends) - it’s a shame to throw it away (used it once), a new battery is very difficult to find + cost of the battery = cost of the flashlight... found a simple solution to the problem…
It is interesting that the lanterns had different operating conditions (by February 23 they were presented to employees) - but everyone died “in one hour.” Naturally it’s a shame, I just needed it, the “new” one is on you too :))) 
Having tried to look for similar batteries in special stores and markets, I came to the conclusion that it is completely inappropriate to buy such a battery for the cost of a flashlight. I couldn’t find a cheap alternative, and besides, the battery characteristics were confusing... That is. 5V was strained when converting to a different type of battery... 
But there was no desire to radically redo the charger and flashlight.
At first there was an idea to plug in 18650 - but the voltage is a volt lower (how the flashlight will light - again alterations... + disassemble/assemble for charging... in short, problems again :(
The solution was found to be very simple - buy an external cheap power bank, which already produces 5V output and has a built-in charging system CHEAP AND TASTY :)
In fact, the original battery had 2Ah. It is clear that in our case there are all kinds of unnecessary losses - but the price justifies the means + some advantages appear :)
Literally on my knees, the flashlight was disassembled, the network connector was removed (the charge was from 220 in the original) and, well, the “interfering wires” - it was actually possible not to touch them :)
Instead of the original battery, I used a power bank with a 2600 can, removed the original cover from the power bank, and secured it with electrical tape so that the structure would not fall apart due to vibrations or shocks.
In fact, everything can be done MUCH more accurately naturally, but I was interested in the simplicity and speed of the solution. 
This is roughly how it turned out (the wiring did not have to be pulled out through the power bank, at first there was an idea for a slightly different arrangement).
Those. I secured the power bank itself by inserting it into the former network connector, even without additional ones. the mount sits quite firmly 
Main advantages:
The lantern is alive!
Quite easy and inexpensive!
It is easy to change the battery (in case of failure) - they are common and inexpensive.
You can charge from any USB (including in a car), and also, if necessary, use it as a power bank (depending on the quality of the latter).
The flashlight shines normally. I didn’t try to time it, but it shines for a VERY long time, probably for several hours, I didn’t try to discharge it at once.
I'm planning to buy +22 Add to favorites I liked the review +38 +71Hi all! Many people have such a flashlight; it is sold in many stores under different names, but its design is the same. It is inexpensive, shines well, but there is a big drawback - it is powered by two R20 batteries, which cost several times more than this flashlight. I want to offer my way to solve this problem. Instead of batteries, I installed a phone battery in the case and removed the charging socket. First you need to disassemble the flashlight, remove the rubber cover from the handle and pull out the spring (terminal "-"). She won't be needed anymore.
Next you need to select a battery; it should fit in the handle of the flashlight. My battery fit perfectly. I attached 2 wires to the battery contacts using electrical tape so that the structure would be dismountable.
You need to solder a resistance to the LED block, because... our battery produces more than the 3 V required by design. You can calculate the resistance using an online calculator. Such LEDs must be designed for a voltage of 3 V and a current of 20 mA.
You can assemble the resulting structure.
At the end of the handle I attach the charging socket using glue.
All that remains is to make a hole in the rubber boot opposite the socket.
Now the flashlight can be used.
Connection diagram.
This modification allowed for significant savings on batteries. Even if you don’t have a battery, its purchase will pay off immediately, because its cost is approximately equal to the cost of 2 normal R20 batteries. In addition, the flashlight works on the battery until the end, then simply turns off, without significantly reducing the brightness. I used a battery that was far from new; the flashlight's operating time was 14 hours.
Literally, the flashlight was disassembled on the knee, the network connector was removed (the charge was from 220 in the original) and the “interfering wires” - You really shouldn't have touched them :)
Instead of the original battery, I used a power bank with a 2600 can, removed the original case from the power bank (there is no use for metal next to the printed circuit board), and secured it with electrical tape so that the structure would not fall apart due to vibrations or possible falls of the phone.
In fact, everything can be done MUCH more accurately, but I was interested in the simplicity and speed of the solution at the time of remodeling.
This is approximately how it turned out (the wiring could not have been pulled out through the power bank, but at first there was an idea for a slightly different arrangement, I did not redo it).
The power bank itself was secured by inserting it into the former network connector, even without additional ones. the mount sits quite firmly
Main advantages:
The lantern is alive!
Quite easy and inexpensive!
It is easy to change the battery (in case of failure) - they are common and inexpensive.
You can charge from any USB (including in a car), and also, if necessary, use the flashlight itself as a power bank. There is a flashlight charge control.
The flashlight shines normally. I didn’t try to time it, but it shines for a VERY long time, several hours for sure, I didn’t try to discharge it at once.
The idea of how to convert a headlamp into a battery-powered one arose a long time ago, this is especially true for fishing and when. Since it is not profitable to constantly buy batteries in our age of mobile phones. So, after thinking about it and ordering the necessary spare parts, which I will describe below, I began to modify the headlamp for batteries with my own hands, using a Chinese circuit with charging. This makes it possible to charge the battery both in the car and from a regular micro USB of a modern phone. I usually order from Aliexpress, although it is possible to find it in stores, but it’s 2 times more expensive.
A very bright and functional headlamp, for such a price, but for some reason I haven’t found one on sale now 
I tried to remake this model as well, but it was a little inconvenient to install the button and the diode plate got hot, so I had to isolate it from the battery with a piece of plastic. But in the end the flashlight works properly
The flashlight was delivered to the post office in 20 days, which made me happy :) .
The idea is very simple and anyone can do it; all you need is a small battery from an old cell phone, it contains a Li-Ion battery with protection. The voltage parameters are ideal, the LED flashlight has a voltage range from 4.5 - 2V, and the 3.7V battery in a charged state of 4.2V has a decent capacity, which can be increased by adding another battery in parallel. You just need to correctly identify the contacts (most have plus and minus indicated), all that remains is to carefully solder the contacts so as not to melt and avoid a short circuit.
The problem with charging via a regular micro USB can be easily solved by ordering a small board costing about 20 rubles. Micro USB plays a very important role in controlling the charging and turning off the ice lamp when the battery is low.
The board has LED indicators that indicate in color when the converted LED flashlight is charging. Thus, the modification of the Chinese headlamp comes down to soldering the wires to the terminals.
Using this board, converting any flashlight to lithium is quite simple, it is only important to know how many volts the battery produces.
Charging board, purchased in an online store with free delivery Perhaps I ordered 10 pieces for myself at once because it is universal and can be used in children's toys.
Battery connection diagram 
In fact, this is a separate board that is used in a power bank, and if you buy an additional USB output, you can charge your phone 
Exploded view of the lantern and the first stage of assembly Now, about the conversion of the flashlight itself to use a battery instead of batteries, most flashlights use 3 AA 1.5 V in size, comparable to a mobile battery, and fits quite well in the main body, you just have to expand the seat. After simple manipulations, having unscrewed or cut out all the excess, we mount all the parts in place using hot-melt adhesive.
LED flashlight conversion diagram 
Solder all the parts in place using a heat gun 
If necessary, you can increase the capacity by connecting 2 batteries 
We get a modernized headlamp with a mini USB input In conclusion: the LED flashlight worked actively for 3 nights on old telephone batteries without recharging. Perhaps it would have been enough for more, I didn’t test it before the cutoff. Lithium batteries do not like to be completely discharged. Overall, very pleased at the cost of 140 rubles. The only thing is that it is very bright, which is not always necessary. I was pleased with the presence of charge indicators on the board. When charging via USB, it glows red when the battery is charged blue.
Almost any flashlight can be converted in this way, the only question is the size of the battery. For example, iPhone batteries are not very practical, and if you tear off the contacts from the connection board carelessly, they will not be soldered.
Do not use lithium batteries if they are swollen - it is unsafe!
It happens that the protection on the board is triggered, and you need to revive it, in this case, apply voltage from the power supply or power bank. If the phone batteries are very old, then the protection of the headlamp will naturally work faster and it will go out. Although batteries from an old Nokia (more than 4 years old) work properly.
On inferior 5 mm LEDs for a 18650 lithium battery. Here the scarf was removed, and in return a homemade one was made on new original (the crystal is quite large) LEDs 2835 1 W 350 mA (for backlighting monitors), they have a positive substrate. But you can also use regular 2835 by changing the polarity to standard. On Ali they cost 3 cents.
When installing a new board, you need to grind down the fastening post flush with the reflector cups; the more we grind, the better the focus in the center without darkening is obtained. The charger is used at 5 V 500 mA in narrow cases, installed at the top under the battery (with parts down), the board with the leads is covered with a thick film - a substrate from the ATX power supply unit and the battery is glued on top of the molecule.
The AMC7135 chip is installed as a driver at 3.2 V 350 mA, 5 LEDs account for 70 mA each, which prevents them from heating up with good light output. The result is a very good quality and durable flashlight that will now last for a very long time.
Another more modern flashlight with mains charging, the internals have been replaced with 18650 batteries and 5 V USB charging.
7 LEDs were replaced with higher quality 5 mm “hat” type ones with a brighter glow. But since the flashlight had two modes, I decided for the future to remake the board for two types of LEDs, 6 pieces of 5 mm in a circle and a central powerful CREE LED or 1 W, it fits there on the substrate just right. In this form, scattered light and beam light are obtained.
The driver is standard on LM358, the current of the central LED is selected within 120 mA, which is quite enough for lighting and practically does not heat the substrate. Heating of the LED substrate will start from 150 mA, but if you use double-sided fiberglass, you can use the second side as a small radiator, although this is still unnecessary, since the luminous flux will be only slightly brighter, but the LED substrate will heat up quite strongly.
I assembled it, checked it, everything fits perfectly under the reflector, it shines quite brightly. The light turned out to be cool white from 5 mm LEDs and slightly warm white from CREE.
Conversion of the "A420" flashlight from LDS to LEDs. A friend asked me to look at the flashlight to see if it was possible to make something useful out of it, since with an LDS lamp it quickly eats up the batteries, and it would be a shame to throw it away.
I looked and thought, the power comes from 4 1.5 V batteries, you can make a flashlight for 1 - 4 26650 batteries, but this only partially solves the problem, a flashlight with LEDs would be more useful. It was decided to leave the batteries, but convert the flashlight to LED.
Chinese penny LEDs 2835 at 3-3.6 V 60 mA were taken as the light basis, the total current was calculated at 640 mA, so as not to overheat the crystal. There is enough light with them, but if you need it brighter, you can install brighter LEDs, and replace resistor R2 on the driver with a variable one, there will be additional brightness adjustment.
The printed circuit board was copied and remade to fit the LM358 driver I liked, the LED matrix stands for the contacts, the scarves were taken from an old monitor board, they fit perfectly. A little later, the board was supplemented with a charger for TR4056, the power connector can be installed on the lid, now you can also install any suitable batteries in the flashlight by screwing the terminals directly to the stands.
The canopy of the T-50A model has also been redesigned.
After testing the operating time of the flashlight from the built-in 26650 5A battery, after a while the LEDs began to blink. I thought it was overheating, but separately from the driver they shined wonderfully and didn’t get too hot. The problem turned out to be the Chinese op-amp LM358, which was once purchased by a party; when replaced with the original, the problem with blinking disappeared.
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