Battery Best Buys – and an easy way of comparing batteries.

Where I used to work, I could buy Duracell Professional batteries at low prices through a buying agency. These prices were comparable with prices available on Ebay.

Why did I buy Duracell? Because I could get, for instance, AA cells, of a good quality, for about 25p. But of late the prices have rather climbed, generally to over 40p, as the adverts at the bottom show, causing me to shift to Energizer, which were available at about 34p (below).

More recently I noticed Aldi’s own line of batteries and, since most of Aldi stuff is of reasonable quality, I thought them worth trying. The question was how to make a fair test.

I resorted to my Lidl battery toothbrush. It takes two AA cells. I inserted one Duracell AA and one Lidl AA. Since the 2 cells are in series, exactly the same charge flows through them. All I needed to do was to test each battery every so often and compare their states of charge along the way.

In fact the Aldi AA cell performed exactly the same as the Duracell AA cell and, since Aldi AA cells are 21p, they are an obvious good buy.

My electric toothbrush (Lidl, not Aldi) draws a current of 200 mA. It has a timer which tells me when 2 minutes’ brushing is up and so it is used for very close to 4 minutes every day. 15 days’ use is 1 hour total use, using, therefore, 200mAh of capacity.

The capacity of batteries depends on the discharge current. At 100 mA, the capacity of a Duracell AA is 2.2 Ah. At a discharge current of 500 mA, the capacity decreases to 1.3 Ah. We might guess that the capacity at 200 mA is about 1.8 Ah, meaning that the batteries will last 9 lots of 15 days, or about 4 months – something that was roughly how long they did last.

Pedantic point from teaching physics. In the army, that thing that you put to your shoulder or have in your hand is a rifle or pistol. Guns are very much bigger things and the collective noun for several guns is a battery.
In the same way one cell is a cell; a collection of more than one cells is a battery.