Call For Battery Capacity Markings

David Greaves

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Battery Markings

In the UK there seems to be no quality control over the standard of dry cell batteries on sale and no requirement for vendors to print a guide to the enegy capacity of their product.

Although the precise definition of the useful energy capacity of a battery is open to debate, there is little doubt that the introduction of one or two standard tests would allow battery products to be ranked with little ambiguity.

Leaking Batteries

Surely with Christmas coming, batteries should not be sold that are going to instantly leak all over the insides of nice new toys?

I purchased some cheap C cells at Lathams. These cost 78 pence for eight, whereas the more usual retail price for C cells is perhaps 60-90 pence each.

Lathams Store, Bridge Rd Potter Heigham Great Yarmouth Norfolk NR29 5JE.

I put two of these cells in my bicycle lamp and cycled home from work, a journey of 15 minutes. All seemed well. However, the next day, when I tried my lamp, it was completely dead and covered in some sort of moisture. I thought I must have left it switched on by accident and that the cheap batteries had leaked. So I put two more batteries in the torch and it worked again. However, on the third day, the situation was the same: the torch was dead and covered with moisture again. I was sure I had not left it on this time.

I took the torch apart and made the following photos of the torch and the batteries I had used. Click for enlargements.

These two are the batteries first put in the torch. They have been left to stand vertically for a day and this liquid has come out the top. Also they have left a mark on the cardboard where they were previously just standing.

These second two are still in the torch. The whole interior and underside of the lid are soaking with liquid.

Experiments

I decided to make a measurement of a so-far unused battery from my original pack of eight. I placed it in a plastic dish in case it leaked during the experiment. I loaded it with 22 ohms for one hour and plotted the terminal voltage every 5 minutes.

Minutes Terminal Voltage
Off load 1.62
0 1.54
5 1.517
10 1.490
15 1.466
20 1.450
25 1.433
30 1.420
35 1.410
40 1.396
45 1.386
50 1.379
55 1.373
60 1.368
Load removed 1.410

The battery has dropped in voltage considerably. The average current was about 60 mA so the battery capacity can only be described as a few hundred milliamp-hours at best. This is considerably less than we might expect from an AA cell and far less than we might expect from a quality C cell.

Immediately after the experiment, the battery did not appear to have leaked. However, a few hours later, one or two small drops of mositure appeared on the battery surface. A week later, the tray contained a about half a cc of runny liquid as shown in the second picture.

A couple of hours after the expriment, these two drops were visable on the battery surface.

One week later a fluid had collected in the bottom of the tray.

Copyright 2002 DJ Greaves.