Replacing 2xAA / 2xAAA alkaline batteries with Li-Ion / LiPo battery?

[m1ch43lzm]

Hi, i have this RadioShack IR thermometer Cat. No 22-170 which takes 2xAAA batteriss, I've tried with NiMH AAA rechargeables but it complains about low voltage, it flashes an "empty" battery and doesn't measure anything, even with freshly charged 2xAAA NiMH, so i have to "borrow" the batteries from my multimeter when i want to use it
I'm thinking abour replacing the 2xAAA batteries with a small LiPo battery that fits inside that space, but the voltage would be too high (4.2v)

I'm open to suggestions on whether i should use an LDO or another type of voltage regulator, or dropping the voltage with 2 diodes in series (regular 1N400x + a schottky diode) would be enough?

[sam_sam_sam]

This depends on weather you are going to have an external power supply you have more options unless you want to use a pouch battery cell and even then you are going to need a three volt regulator ic chip or you use an 18650 Lipo 4 battery cells and you would not need a regulator ic chip but would need a BMS board because your operating voltage once charged is 3.4 volts two regulator AA battery cells are 1,56 volts each so you would not need anything else

[m1ch43lzm]

A 18650 wouldn't fit, I'm thinking more about a small lipo cell like this, it needs to fit within the space for 2xAAA

I could charge it with a TP4056 board, the remaining space would be for the voltage regulator

About Lifepo4, I can't find those anywhere in the local shops, only regular 18650 li-ion and those small lipo cells of different sizes and capacities

I think a 10440 lifepo4 would fit, but can't find those locally

Importing those, they're classified as "dangerous goods", but a device containing lipo batteries is fine

[stj]

open it and see whats inside,
it may be more tollerant to voltage swings than you think.
it may also use a couple of resistors to set the low voltage warning level.
if it can tollerate 4.2v then you could use a disposable vape off the street to fix it

[CapLeaker]

open it and see whats inside,
it may be more tollerant to voltage swings than you think.
it may also use a couple of resistors to set the low voltage warning level.
if it can tollerate 4.2v then you could use a disposable vape off the street to fix it

Exactly this!

[m1ch43lzm]

You guys want pictures of the inside, so here they are:
Only interesting ICs are:
- 93c66 EEPROM
- The main blob IC
- There's a header for calibrating it seems

The battery terminals go to a nearby 100uF cap, then go somewhere else on the bottom layer of PCB

if it can tollerate 4.2v then you could use a disposable vape off the street to fix it

If i ever find one, people here only use rechargeable vapes, and regular cigarrettes, i have a small 200mAh 502025 lipo cell, and another smaller one 150mAh, i can get those for around $3-4

I did some tests with the bench PSU
2.4v: Screen lights up with empty battery icon, cannot measure temp
2.5v: Same
2.6v: Battery icon shows half battery, can measure temp (defaults to F, there's a button to change to C)
2.7v upwards: Battery full

So it's almost useless with NiMH batteries, i tried again with another pair of AAA NiMH measuring 2.68v in series and it works, but same batteries work fine on a wireless mouse down to 1v each

[m1ch43lzm]

Pictures of the lipo cells I have, the bigger one fits on the battery compartment with some space left
Noticed that the forum ate my picture on post #3, reuploaded here

[eccerr0r]

2xAAA = 3V @ 1Ah
2xAA = 3V @ 2Ah
1 LiPoly = 3.7V @ 0.2Ah ... so... which will last longer...

TBH if I didn't stay with alkaline, I'd look for those integrated lithium ion batteries that have a buck/boost in them

[m1ch43lzm]

2xAAA = 3V @ 1Ah
2xAA = 3V @ 2Ah
1 LiPoly = 3.7V @ 0.2Ah ... so... which will last longer...

It's not about runtime, as that IR thermometer is seldom used, if the battery goes flat (ok, not too low but around 3.2v-3.3v for a LiPo) it can be charged with a TP4056 board
The NiMH AAA i have claim 900mAh, but as I said before, the IR thermometer doesn't like them if they get "too low"
As I use alkaline batteries myself on the multimeter, last time i changed batteries on it was about 5 years ago and the multimeter still works today (no low battery warning yet)

The plan is to not waste money on alkaline batteries, as I use NiMH AAAs on the wireless mouse and keyboard, they last about 5-6 months
Same fon an electric toothbrush, 2xAA NiMH instead of spending money on alkalines
I also have a UV flashlight which I use for curing solder mask, it came with a holder for 3xAAA, i modded it to a single 18650 battery taken from a cheap powerbank
The TV remotes get whatever leftover batteries i find until they don't work anymore, and the cycle repeats

TBH if I didn't stay with alkaline, I'd look for those integrated lithium ion batteries that have a buck/boost in them

You mean those? https://www.aliexpress.com/item/1005009089552500.html
I doubt the claim of "3000" mAh, i'm guessing more like 300mAh, aliexpress claims free shipping

[sam_sam_sam]

You mean those? https://www.aliexpress.com/item/1005009089552500.html
I doubt the claim of "3000" mAh, i'm guessing more like 300mAh, aliexpress claims free shipping

The website link is not valid unfortunately

[m1ch43lzm]

sam_sam_sam Works for me


EDIT: On my phone it opens the aliexpress app
EDIT2: Amazon link for similar batteries, they have a type-c port on one end, unfortunately for me amazon doesnt ship those to my country
https://www.amazon.com/CARDIENS-Rech...dp/B0DFMQ2ZLB/

[eccerr0r]

Look for some other ones, that's definitely not 3000mAh.

I'd probably take the batteries out of devices that leak a significant amount of energy and only put them in when needed...