The battery in the freezer

You need

• From the drawer: the multimeter, two alligator clips, a zipper bag, the freezer.
• To buy: a fresh alkaline AA and a 10 Ω, 1 W resistor.
• Optional: an 18650 lithium-ion cell, with its own 10 Ω, 5 W ceramic resistor.

Do

BeforeThe 10 Ω at 1.6 V passes 0.16 A and dissipates 0.26 W: the 1 W stays warm. On an 18650 at 4 V, 1.6 W: the 1 W chars, the 5 W burns if left connected and forgotten. Five seconds under load, never more. Never short a battery: an AA delivers several amps and leaks, an 18650 delivers tens of amps and can catch fire. On the 18650, the positive button nearly touches the rim of the can, the negative: a clip that slips makes that short; clips on before the resistor, and held in the hand. The battery frosts over as it comes out; water does nothing at 1.5 V, wipe it before storing. A cold lithium cell is not recharged until warm. A pack goes neither in the freezer nor on the 10 Ω (at 56 V, 5.6 A and 300 W): open circuit at its terminals, under load in its tool.

1. The resistor on the ohmmeter, leads shorted together first and their 0.2 to 0.5 Ω subtracted: 9.5 to 10.5 Ω. Write down R.

2. The multimeter on the 2 V range, the same from V1 to V4. The warm battery, an hour in the room, at open circuit: V1.

   expected1.58 to 1.62 V fresh; 1.50 to 1.55 V already used, with a 0.06 to 0.15 V drop at step 3

3. Clips on the resistor, then on the battery; probes on the metal of the terminals, button and base, never on the clips (0.1 Ω of contact, as much as the drop itself); read at five seconds, disconnect: V2.

   expected1.54 to 1.58 V, 0.02 to 0.05 V below V1. The current, V2/R, about 0.155 A; the internal resistance, (V1 - V2)/I: 0.15 to 0.35 Ω, around 0.25 Ω

4. The battery in its bag, in the freezer, overnight, at -18 °C.

5. The battery out of the bag, at open circuit, within the minute, without warming it with your fingers, probes pressed through the frost: V3.

   expected1.55 to 1.60 V, a few hundredths below V1

6. Under 10 Ω, same minute, read at five seconds: V4.

   expected1.35 to 1.50 V, 0.10 to 0.25 V below V3. The current falls to about 0.14 A; the internal resistance climbs to 0.6 to 1.8 Ω, around 1 Ω, four times the warm battery

7. Optional, the 18650 on its 10 Ω, 5 W, same probes. Warm, 3.6 to 4.2 V at open circuit, and 0.01 to 0.03 V of drop under 10 Ω, 0.03 to 0.08 Ω, readable only at the millivolt (6,000 counts, 6 V range); on 2,000 counts the display says "less than 0.02 V". Cold, 0.05 to 0.15 V, 0.15 to 0.4 Ω, readable on any meter. Same slope, nearly an order of magnitude lower.