I am trying to replace the battery of a rechargeable LED torch, but it looks different than most others that I have seen. I was wondering if anyone can help me identify it, so I can try to find a replacement. Otherwise I'm thinking I'll replace it with an 18650 and a TP4056 (mini USB dc charging), but an in-place replacement would be good. It recharges from Mains power, if that helps. I opened a couple of others of different make but similar form, and they all had similar looking batteries.

The yellow caps are kinda like silicone I think, and not solid. The battery voltage is ~3 or 3.5 I think, and the LEDs are very dull. The source of the torch is India. But essentially Mains is 220V.

The battery is very similar to this 4V 0.5Ah lead acid battery

enter image description here enter image description here


closed as off-topic by Chris Stratton, Nick Alexeev Aug 4 at 15:33

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  • \$\begingroup\$ This is not a safe project to attempt. Replace the entire light with a properly engineered product of higher quality. \$\endgroup\$ – Chris Stratton Aug 4 at 15:30
  • 1
    \$\begingroup\$ @ChrisStratton I think replacing the battery AND the charge controller AND the source of light by a properly protected Li-Ion battery, a properly design Lithium charger and switch-mode constant current source, and a white LED would be quite a nice project. But yeah, of this whole thing, the case and the reflector might be salvageable, probably at a cost much higher than that of a new flash light. \$\endgroup\$ – Marcus Müller Aug 4 at 15:35
  • \$\begingroup\$ What mains voltage ? Mains AC direct to torch? For interest, where are you located. (Massachusetts is one guess :-) ). \$\endgroup\$ – Russell McMahon Aug 4 at 16:46
  • \$\begingroup\$ @RussellMcMahon the source is an entire planet away in india. I believe mains of 220V is connected to the PCB above the battery which is then charging the battery. \$\endgroup\$ – Karthik T Aug 5 at 3:30
  • \$\begingroup\$ @RussellMcMahon Im curious, why Massachusetts? :) \$\endgroup\$ – Karthik T Aug 5 at 3:52

The following (as edited :-) ) IS good advice.
Whether it is worth following, is up to the original poster or those who come after. Do please note the clear warnings re potentially ** lethal voltages probably present in the original device. These will not be present if a 5V USB type power supply is used, as recommended, in the new design.

The battery is "almost certainly" a two cell "4 Volt" lead acid one.
These are not common but I have seen Chinese made lights using similar.
The design is probably very old (I'd love one), the LED is probably low efficiency and low output and the charger is probably lethally dangerous. If that doesn't stop you, read on.

The battery can probably be replaced with an 18650 or other LiIon single cell battery. These have lower low end voltage than the Pb battery - which may be a problem if their circuitry purposefully drops some voltage using eg series diodes or a voltage regulator with more than a few tenths of a volt dropout voltage. (Use of a regulator is unlikely.
A simple series resistor would probably replace the "electronics" previously used (if any).

Recharging is more problematic.
The mains charger will destroy the liIon battery unless limited to say 4.0V ABSOLUTE MAXIMUM. You can float a liIon cell at 4.0V with some hope of an OK lifetime but NOT at 4.2V.

A good alternative choice is to use one of the many many TP4056 LiIon charger modules available on ebay / AliExpress. These accept 5 to 6V (preferably 5V) and handle all charging aspects.
Modules with an inbuilt output protection/cutoff feature cost little more and are a good idea.

Identifying what sort of charger is currently in use.

There are strong indications from the photo that the existing charger is a dangerous "AC mains input series capacitor" type. This is covered below, but 1st I'll mention the possible alternative.

Low voltage charger: - IF the charger uses a "plug pack" / wall wart" with a low voltage output of say 5VDC to 6VDC it may be able to be used for a LiIon battery - see below. If not, adding one would be (very) wise.


If the cord that connects to the torch carries AC mains (110 VAC?) then the following applies.


The markings on the capacitor used indicate that it is a 0.68 uF 400V rated part - indicating that this is almost certainly a mains voltage charger. (Such as part is almost certainly not used in a low voltage charger).
Be aware that IF you input AC mains to the on-body connector then it is almost certainly a capacitor impedance voltage dropper type that will kill you if you let it - consider ALL connections always at MAINS VOLTAGE with that sort of supply.

If it is a mains input charger the best choice would be to change to a regulated 5VDC plug pack (such as used for most modern cellphones) and proceed with the TP4056 advice.

If you MUST try to adapt a lethally dangerous AC mains capacitor charger (Hint: Don't!) then you need to establish Voc and Ichg. Charge current is probably 25 or 50 mA half/full wave on 110 VAC and about double that on 230 VAC. Too low really. I'll not give more advice on that here - ask if still interested in that aspect.

Low voltage charger

If adding one, use a 5VDC one rated at up to 1A.

If the existing input is low voltage DC (unlikely)

  • Measure the voltage O/C (open circuit) from the inbuilt charger.

  • If OC voltage is >= 5V and under about 6V or maybe 7V it will operate the TP4056 Ok.

  • Loaded it should be 5V optimum and not over 6V for thermal reasons. The modules are resistor programmable for charge currents of <= 1A.

  • If Voc is > about 7V it will need to be regulated or resistor loaded to bring it under 7V OC.

TP4056 chargers:

ebay TP4056 charger search

Avoid this style - only $2.99 for 10! BUT does not have battery cutoff feature - battery output only - no separate load terminals.

Aim for this style

Note separate Out-/Out+ and Battery - / Battery + connections.
Vin can be via microUSB connector or +/- terminals on other side of it.

enter image description here

Here is an SE EE question related to the TP4056 modules.

TP4056 circuit with and without low voltage battery cutout protection.

This is a typical module circuit diagram:

The simpler modules omit the DW01-A protection IC and the FS8205A back-to-back MOSFET switch and connect B- to Out-.

Simple module: Relatively complete LiIon charger with up to 1A output current.
More complex module: As per simple module but adds a battery over-discharge protection function.

Given the very small difference between the modules, use of the module with output protection is by far the best choice.
The battery connects to B+ and B-. The load connects to Out+ and Out-.
That's it ... .
TP4056 IC datasheet here.

A web page on TP4056 charging performance under various conditions here

enter image description here

  • \$\begingroup\$ This is bad advice. The device cannot be safely repaired or re-engineered by the asker with a lithium battery and it is irresponsible to suggest that they could. \$\endgroup\$ – Chris Stratton Aug 4 at 15:27
  • \$\begingroup\$ @ChrisStratton Your cautions are noted. "Cannot" and "safely" are such strong words :-). I've upgraded my already non-trivial safety warnings, and "very highly recommended" [tm] that a 5V USB plug pack and TP4056 module be used. || At that stage he has a clunky torch with old LED, probably. It may or may not be an attractive mod. It can be done and its safe. \$\endgroup\$ – Russell McMahon Aug 4 at 16:40
  • \$\begingroup\$ I actually do own a TP4056 already, and I was considering using it here. I prefer the option to charge via USB, and it is safer as well in my mind. \$\endgroup\$ – Karthik T Aug 5 at 3:31
  • \$\begingroup\$ The torch has a pop out plug which plugs directly into the mains, so no transformer other than what is on that circuit board. The back of the plug is visible in the top right part of the images. \$\endgroup\$ – Karthik T Aug 5 at 3:36
  • \$\begingroup\$ Marking as the answer because the identification seems right.. I was able to locate it, aliexpress.com/item/32860027654.html \$\endgroup\$ – Karthik T Aug 5 at 3:42

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