There is no soldering to make this extremely easy tiny battery tester..

You can keep the tester in your very smallest pocket..

Take a careful look at Battery caused LED brightness.

And there are other uses for these component parts.

Step 1: Parts

Wondermagnet.com supplied the NdFeB Neodymium-Iron-Boron Rod magnets for this project.

Top magnet ¼"dia × ¼ "long rod
Base magnet ¼"dia × ½"long rod

Safety Notes

Please do not let little children play, mouth, or risk swallowing these attractive magnets,
a serious surgical situation may result if swallowed.
Also take care to restrict access to the little button batteries which may contain mercury.

I take no responsibility for any mishap, or injury that may result or occur now or at some later time because of this project..

Step 2: LED INDICATOR

Electronic Goldmine is
A supplier of surplus electronics and has a 5mm White LED for under $2 for you
Any white or blue LED will do.

A red led will be damaged testing the DL20xx 3 Volt lion button batteries.

Use a tweezer or a small needle nose pliers to form the flat curl on the positive Anode LED lead..

Step 3: Theory

You can skip this step..... if the theory does not interest you...

The two NIB magnets not only pinch the curled Anode LED lead wire between them but the
magnet's nickle plating readily conducts the electricity.

This means the steel positive side of the 1.5 Volt cell battery conducts current to the LED Anode.

The steel positive button battery is held in place by the NIB magnetic attraction
which is strong enough to grapple a second cell on top and in electrical series ..

The necessary voltage to light a white or blue LED is in excess of 2 Volts and sometimes 3 Volts or more..

That is why this tester uses two button batteries and a white LED

You may wonder why the white LED has a prominent blue ring around the strong white ?
Two Reasons ;

A white LED is actually a blue LED with red and green phosphors. RGB = White..
This is a cheep poorly manufactured white LED and too much of the blue light leaks out.

Now you can discern for yourself quality white LEDs from scrap ones :¬)

NIB = NdFeB Neodymium-Iron-Boron

Step 4: PUT IT ALL TOGETHER

Start with a new 1.5 Volt fully charged button battery ( see picture # 1 ) any diameter and
put it on the short rod magnet ( see picture # 2 ).

Now put the LED curled wire loop between the other end of the magnet and pinch it with the
longer rod magnet ( see picture # 3 )..

Testing a coin battery is as simple as ( picture # 4 ).

The top battery is the one that is on test.
The bottom magnet is longer in order to provide holding room for adult fingers.

To view used and dead batteries go back to Step 1 and look at the picture notes.

Step 5: OTHER APPLICATIONS

A head light is demonstrated for conceptual relevance.

Take a sweat band and use the two magnets plus a 3 Volt DL2032 Cell as pictured..
You will need to bend the LED leads ( easy by hand ) to pinch the battery and point down..
Use longer rod magnet to capture the Anode LED wire curl to the + battery as in the last pic..
Then use the short rod magnet to hold the assembly to the sweat band...

See a last moment application of the repurposed battery tester to a working LED
head band in a darkened room illuminating other electronic gear.

You can make ;.

A Head light
A bicycle light
A Throwie
A locator beacon
A wrist light
A flash light
A garden light
A Lantern
An accent light
And a mini battery tester

You may wonder why the white LED has a prominent blue ring around the strong white ?
Two Reasons ;

A white LED is actually a blue LED with red and green phosphors. RGB = White..
This is a cheep poorly manufactured white LED and too much of the blue light leaks out.

Now you can discern for yourself quality white LEDs from scrap ones :¬)