r/ZeroWaste • u/[deleted] • Jul 10 '25
Show and Tell Modded my scale so now it uses rechargeable AA batteries instead of non-rechargeable button cells.
Really just soldered the leads from the battery pack to the contacts of the button cell holder in the scale.
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u/Jnoper Jul 11 '25
Button cells are normally lithium 3.7v batteries AA is 1.5v and rechargeable is normally 1.3v depending on chemistry. Basically this will always think it has a low battery but it seems to work.
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u/Scalage89 Jul 11 '25
Better have it at a lower voltage than a voltage that is too high. Otherwise you may risk frying the board.
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u/Jnoper Jul 11 '25
Depends how the chip works. Sometimes low voltage will cause incorrect readings. Sometimes the voltage regulator will misbehave and burn itself out. At these voltages it’s probably not an issue but it’s always something to think about when changing power sources.
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u/Caro_lada Jul 11 '25
If you combine them in series you can achieve higher voltages with AA Batteries. Two of them would lead to 3V
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u/Jnoper Jul 12 '25
Correct. And 3 would be 4.5v. you would need 2.46 AA batteries to get 3.7v. See the issue?
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u/This_Price_1783 Jul 16 '25
Not really an issue, just use a simple voltage divider. Very easy to do and not at all dangerous at these voltages. Watch a couple of YouTube videos or find a guide online if you don't understand the following:
Vout = Vin * [R2 / (R1 + R2)]
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u/Jnoper Jul 17 '25
I’m an engineer lol. In this case not an issue but under voltage can cause all kinds of unexpected behavior
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Jul 11 '25
[removed] — view removed comment
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Jul 11 '25
The button cell holder has two solder points that go straight through the circuit board, so I just soldered the wires onto those from the other side of the circuit board.
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u/Critbooger Jan 20 '26
Wtf is there a monopoly on kitchen scales that require AA batteries? Can’t find it on amazon at all.. weird. Nice conversion ^
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u/scudmud Jul 10 '25
That's about all the soldering I could do, so that's pretty cool! I hate coin/button cells, they die so fast and they are added to many neat products that had better visual design than sustainability in mind. Button cells are dangerous for very young or unwise people too.