Testing alkaline batteries Featured

It's probably only calibrated for the former but by putting a resistive load across the battery during the test will bring the voltage below

An alkaline battery also has a nominal o/c voltage of 1.5V

Internal resistance is a good indication of battery capacity, and the easiest way to measure this is under load.

Alkaline are also 1.5v. You are thinking of rechargeables (e.h. NiMH) for

That is clearly not so, since most of them have 1.5v, its only rechargeable nicad or nimh that have 1.2v.

The normal way I test batteries is with a load, If you blip a reasonable load on a good battery, no change in volts, on a partly dead one there is a drop, as the area used is smaller, ie it cannot shove out the same current as its electrodes get coated. Most alkaline if used a little, charged a little etc can last a surprisingly long time before the system cannot hold the charge. Beware though as the seals can go with the pressure inside if you get too greedy. Brian

Thanks. This certainly explains it. I was indeed mistaken.

Alkaline are also 1.5v when new.

It's rechargeable NiCd and NiMh that have a lower 'good' voltage, around 1.2 to 1.3 volts.

Indeed, mea culpa.

There are 2 requirements for a good battery: voltage & current. Terminal voltage often tells enough, but not always. The other test is to touch probes of a 1A meter to the battery for a fraction of a second, see how fast the needle flies up. Digital meters generally can't do this. Keep the probes on & you'll kill both meter & battery.

NT

A common AA alkaline battery might have anywhere between 0.1 ? and 0.9 ? internal resistance."

The Energizer method uses two load resistors, first tests with the light load, then light+heavy load.

Paul

I used to love winding up car boot sellers, flogging batteries. I would ask them for SR44 camera batteries, and they would always try and flog me LR44's, "because they are the same".

When asked what their understanding of current delivery characteristics is, they would get into the usual nonsense claim that they "would work", which in many cases they wouldn't.

A good fresh alkaline can be as high as 1.6v open circuit.

Most battery testers are based on presenting a load to the cell and then measuring the voltage under that stress test. Some Duracells had a self test feature at one time - but it made them much less reliable :(

I no longer use Duracells I have had too many leaks. Panasonic and Energiser are my preferred brands now for things where rechargeables won't hack it. Usually low current draw LCD display devices.

Could my battery testing facility (in the multimeter) be doing this?

Given that a humble AA can source 10A into a dead short that would quite likely wrap the needle round the end stop on an analogue meter or blow the internal fuse on a modern digital meter.

It probably measures the battery terminal voltage with and without a suitable load resistor across it.

I have a cheapo meter that can handle 20A. Combined with the resistance of the test leads I think it would be quite safe for the meter. The leads might get warm though!

It might but you need to look at the instructions/spec of your meter to confirm.

I don't have a meter with this facility, nor have I seen a multimeter that has.

You'll most likely blow the fuse in the DVM if the battery can exceed the current range.

They start off above 1.5v. 1.5v is only nominal.

A well used one can go as high as 1.8v under odd circumstances. I had a couple do that earlier this year. They were well used then recharged, and gave a strangely high output. No idea why, none of the others did.

NT

that's why it's only connected for a fraction of a second. What you're looking for is enough oomph to be confident the needle would fly off the end if it stayed connected. Harmless if not sustained. You can't use the method with digitals.

A load resistor yes, how suitable is another matter. They tend to load them very lightly.

NT

If anything gets warm you left it connected way too long.