Use voltage to determine remaining charge in a used AA alkaline?

[Baggas]

When I remove some old alkaline cells (AA or AAA) from a device, I sometimes check their voltage.

Although a cell measured in that way has no load, is it very roughly possible to use voltage to know how depleted it is?

Some of my devices need fresher cells than others and I was thinking if the voltage (indicating charge) of a used cell was high enough, then I could keep the cell for other devices when needed.

 

[Lynx_Arc]

If the alkaline is a "normal" variety you can get a rough estimate in that from 1.5 or higher voltage is near or full capacity when it drops to 1.3v it is from about 10-30% capacity and below 1.1v it is probably less than 10% capacity.
The problem is without a load some alkalines will measure higher than others and have less capacity. Batteries that aren't alkaline at all can be mistaken for them can be impossible to guess how much they have left in them. I had one such battery that came with a remote that measured 1.6v with no load that the remote started acting up and I couldn't figure out why it would work for a few presses then stop working and waiting for a few hours work again for awhile and stop. Under a load the battery caved to below 1v. In other words it is better to have a load on a battery and with no load if it measures 1.3v then likely under any load it may fail to work properly especially in devices that nimh don't work well in.

 

[aznsx]

When I remove some old alkaline cells (AA or AAA) from a device, I sometimes check their voltage.

Although a cell measured in that way has no load, is it very roughly possible to use voltage to know how depleted it is?

Some of my devices need fresher cells than others and I was thinking if the voltage (indicating charge) of a used cell was high enough, then I could keep the cell for other devices when needed.

In addition to Lynx-Arc's comments, here's another suggestion which might help others, and those who might be buying a DMM. Many DMMs have a 'Batt Test' function which measures voltage while applying a load to ~1.5V cells, and some also have a setting for ~9V batts. Some good but relatively inexpensive meters incorporate this function, and if you use such cells / batts regularly, one might want to opt for such a DMM when shopping. My 'kitchen drawer' DMM is this Extech model, which offers both:

MN15A: Digital Mini MultiMeter | Extech Instruments

MN15A: Compact Manual ranging multimeter with 8 functions including Temperature. Experience the Extech Advantage

www.extech.com

Extech's claim to fame (mission statement) is relatively high quality test equipment at relatively reasonable prices (high value), and I can recommend them. I don't know the exact load resistance it applies (not stated in specs), but I'd trust Extech to pick an appropriate value. Just a thought when one is shopping for a general purpose meter. Their other models likely incorporate this feature too...

 

[Lynx_Arc]

I didn't think of measuring the resistors in my battery tester when I took it apart to mod it to take 18650s. It has 3 levels you can use if you knew the right resistors to test various battery types you would be able to do it without a battery testing gadget.

 

[idleprocess]

Energizer publishes data on their cells. Taking a glance at alkaline AA cells, looks like 0.8V operating is the cutoff for the E91. However that's not an open-circuit (non-operating) measurement.

A number of ... sources ... I'm finding (ie. CNN of all places) are split on 1.4V and 1.35V open-circuit voltage as the effective zero point for alkaline cells. The general shape of the discharge curves for loaded cells could be used to roughly approximate percentage remaining so long as you adjust the endpoints (100% 1.65V / 0% 1.35V) and the different relative range.

 

[Baggas]

My 'kitchen drawer' DMM is this Extech model, which offers both:

MN15A: Digital Mini MultiMeter | Extech Instruments

MN15A: Compact Manual ranging multimeter with 8 functions including Temperature. Experience the Extech Advantage

www.extech.com

Extech's claim to fame (mission statement) is relatively high quality test equipment at relatively reasonable prices (high value), and I can recommend them.

I've been looking recently for a basic multimeter but got ovewhelmed by the torrent of Chinese models all claiming improbable "mega" specifications but probably built out of the cheapest components imaginable.

I'll take look at the Extech range you mention. Whilst they're also probably made in China there may at least be some western quality control being applied somewhere! see there's an Extech MN25 for £29 or an Extech MN36 for £34 on Amazon UK. There's quite a big range on the main Extech web site, which does rather hint at dreaded Chinese involvement!

http://www.extech.com/categories/digital-multimeters/general-purpose

 

[LEDphile]

Probably worth moving the multimeter question to a new thread, but Extech is a reasonably well known purveyor of entry-level measurement tools. My experience has been that their products are serviceable, but not up to the same level of refinement as the name brands.

One thing to watch for on most of the low-cost multimeters is that they are usually Category II devices or below. This means that they are intended for use in controlled, energy limited environments, and are not suitable for measuring mains voltage. For applications involving things like alkaline batteries, this isn't typically an issue, but is something I'd be concerned about for a general-use device. Personally, I'd want at least a 300V Category III rating for a general-use DMM (Fluke has a reasonable writeup on the differences between the categories https://www.fluke.com/en-us/learn/blog/safety/multimeter-guide ).

 

[Baggas]

One thing to watch for on most of the low-cost multimeters is that they are usually Category II devices or below. This means that they are intended for use in controlled, energy limited environments, and are not suitable for measuring mains voltage.

I just noticed Amazon is now selling their own brand multimeters. Do you have any thoughts about them? I've generally been happy with their own products. However, there's no mention I could find about "CAT".

See https://www.amazon.co.uk/dp/B083V7BMZR/

Fluke meters are out of my league cost-wise!

 

[Baggas]

A number of ... sources ... I'm finding (ie. CNN of all places) are split on 1.4V and 1.35V open-circuit voltage as the effective zero point for alkaline cells.

I would be interested to read that discussion. Do you have a link?

 

[Dave_H]

Have a look at Wikipedia. There is a table part way down with loaded/unloaded AA voltages which should be somewhat useful.

Alkaline battery - Wikipedia

en.wikipedia.org

Dave

 

[Dave_H]

Energizer publishes data on their cells. Taking a glance at alkaline AA cells, looks like 0.8V operating is the cutoff for the E91. However that's not an open-circuit (non-operating) measurement.

A number of ... sources ... I'm finding (ie. CNN of all places) are split on 1.4V and 1.35V open-circuit voltage as the effective zero point for alkaline cells. The general shape of the discharge curves for loaded cells could be used to roughly approximate percentage remaining so long as you adjust the endpoints (100% 1.65V / 0% 1.35V) and the different relative range.

1.35-1.40v sounds high for "zero point". I would consider 1.0-1.2v where capacity estimate is below 20% to be a better measure, but of course depends on application drain.

I discharge lots of cells even below this albeit at low rate. Small 4AA LED lantern runs on cells 0.8v or lower for several nights as a nightlight. Light output is low but that suits the situation. Occasionally one leaks but it's a cheap light and just gets cleaned up.

Dave

 

[Dave_H]

End point does depend on loading, and judging from the recovered alkalines with resting voltage 1.3-1.4v+ I have been finding, some high-drain devices are leaving behind a fair bit of capacity when their users discard them.

I have a small 2AA FM radio, and 3AA amplified speaker hooked up to MP3 player. End point for these is when audio drops and starts to get distorted (voice only, not high fidelity) just above 1v/cell.

Dave

 

[Dave_H]

I know this pushes end-voltage beyond what most consider useful, but with D cells I wired a 2D holder which put two in series which are below 1v, to power a solar garden light which normally runs from one cell down to 0.8v- 0.9v. Another case is small 2D closet light (or flashlight) which has Dorcy 1-2 cell LED bulb installed. Both cases provide useful nightlight and utterly drain the cells.

Dave

 

[Lynx_Arc]

I know this pushes end-voltage beyond what most consider useful, but with D cells I wired a 2D holder which put two in series which are below 1v, to power a solar garden light which normally runs from one cell down to 0.8v- 0.9v. Another case is small 2D closet light (or flashlight) which has Dorcy 1-2 cell LED bulb installed. Both cases provide useful nightlight and utterly drain the cells.

Dave

I've done similar. I picked up a 1D energizer light with an LED dropin in it and put it in a 2AA light and am using 2 nimh AAs in it with no problem. I think at one time dorcy LED dropins were 1-6 cell rated.

 

[Dave_H]

Dorcy "30-lumen" is 1-2 cell with boost circuit in the base. "40-lumen" 3-4 cell seems to use just a dropping resistor or other simple current regulator.

Dave

 

[Timothybil]

I have a Mini-MBT battery tester from ZTS. It uses a pulse load process to determine the remaining power. It uses LEDs to indicate one of five power levels, with the lowest being 'essentially dead.' Besides just testing individual cells I have used it to pair up partial cells I have laying around when I need more than one for a device. Since it uses tailored programs for different cells, they offer several different models based on which cells they test. Worth the money.