My Dad showed me how to do this, when I was a boy. Take a
flash light bulb (PR-4 is good, the old screw in 112 is
better, more close to the proper voltage). Then, take about
six or seven inch long piece of #10 or #12 solid wire. Wrap
one end of the wire around the bulb. Curve the rest of the
wire, so it looks like a letter C, or G.

Touch one end of the battery to the lead spot, on the bulb.
Touch the other end of the wire to the other end of the
battery. If the bulb lights, the battery is OK. Works for
AAAA through D cells. Have to bend the wire a bit, for
different sizes.

After using this for a while, you can also roughly guess the
battery state. New, used, weak, dead. By how bright the
light is.

--
Christopher A. Young
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