I have a device (the wii "sensor" bar, basically an IR LED array) that the literature says takes 7v. I can't find any battery offerings that come in 7v, but many that are 3.7v, so I am stuck trying to find some other solution.

Optimally, I want to create a rechargeable battery pack that is cheap and can give me those 7v, while also being small and practical (no 4x AAA for example).

I am considering three different options.

I have a 12v A23 cell, so perhaps a rechargeable A23 cell stepped down to 7v. But I have little knowledge and no experience with step down converters.

Another option is to connect two 3.7v batteries in series, but I read in a comment that this would require a balancer, because otherwise one of the cells might, uh, burst when charging. I had not heard about a balancer before, but I have an old laptop battery with 18650 cells that I had taken apart and it seems to contain a component that looks like that's what its purpose was.

The last option is to use a 5v source (like a small power bank) with a step up converter. But again, little knowledge and no experience on the matter.

So how should I go about it? I have lipo charger boards (I think they are TP4056) that I got some years ago and could probably use for this, and a cheap dollar store powerbank that uses an 18650 cell with usb connectors (but it gets really hot).

Any help or direction would be greatly appreciated.

  • 4
    \$\begingroup\$ I would use a single lithium ion battery and a step up voltage converter. \$\endgroup\$ Mar 4 at 0:20
  • 1
    \$\begingroup\$ @user1850479 a single cell, not a battery \$\endgroup\$
    – jsotola
    Mar 4 at 0:54
  • \$\begingroup\$ Would voltage matter when it comes to the cell to be used? \$\endgroup\$
    – insaner
    Mar 4 at 1:21
  • 1
    \$\begingroup\$ Post a link to that Led array. Maybe a current drive (not voltage) is a better option. \$\endgroup\$ Mar 4 at 2:05
  • \$\begingroup\$ FWIW, Google turns up people saying you can power the 7V sensor bar with an ordinary 9V battery. Pictures show a series resistor, so I suppose it just gets slightly brighter. A step up converter (or just changing the resistor) is definitely cleaner though. \$\endgroup\$ Mar 4 at 2:18

1 Answer 1


Simple current limitter bellow:

This do the job much effectively then simple resistor limitter on Wii board. A Led current fluctuates much less over battery voltage change.

You have to remove/short the 74ohm resistor on Wii board since the current limitting do the transistor.

This limitter holds a constant current in all battery range (8-10V) in about 10% precision.

The Led current is set by Rx according formula on papper. (For 20mA led current try Rx=33ohm)

enter image description here

  • \$\begingroup\$ Hi Michal, thank you for the answer! I might have to do some reading to understand everything you've written there, but I did want to ask, when you say "wii board" do you mean the pcb of the sensor bar? What I am hoping to do is not open the sensor itself, rather just create a small attachment, about the size of a small battery, and connect that to the sensor. \$\endgroup\$
    – insaner
    Mar 18 at 5:37
  • \$\begingroup\$ If you don’t want to open the sensor to remove the resistor rather use 9V battery + 7 or 8V LDO (low dropout regulator). \$\endgroup\$ Mar 18 at 6:18

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