When is an AA cell considered as discharged, and how long should they last?

[ericmark]

The cat flap started flashing a red light, and the cat could not get in, so temporary fix was insulation tape over the catches, until I could get new batteries. So now four new AA cells and only our cats with the chip can get into the house, plus anything they help in by carrying it in their mouths, moles, mice, birds etc.

So measured old batteries at around 1.15 volts each, all Duracell Power Boost, not worth fitting cheap batteries for this job, the Optimum not on sale in local Morrisons. Same applies with TRV heads and wall thermostats, best quality used.

They have lasted around 9 months, so not too bad, but if cats can't get in, they stop going out, so important it does not fail.

But, years ago we realised the Duracell was a better quality battery, but today we have Power Boost, Optimum, Plus, Procell, Classic, and Simple. All are made by Duracell, with 70%, 100%, 150% and 200% being quoted, but it seems no watt/hour etc is stated.

The removed batteries say Optimum 03/2034 new ones Power Boost 03/2035. I just selected the most expensive. £9 for 12.

Was it worth it? Or would Morrisons own at £6 be just as good?

 

[JohnD]

9 months suggests it is not a high-drain device, so you don't need expensive lithium.

Extracted from the October 2026 "Which" report....

--------------

Best Buy/Great Value: Tesco Extra Long Life AAA
Our score and verdict 78%, Better than most branded batteries
Available from Tesco (£3.50 pack of four)
Pros
Excellent in all types of devices
Value-for-money
Cons
Shorter life than more expensive lithium types

-----------------

Best Buy: Sainsbury's Home Long Life Alkaline AA
Our score and verdict 77%, Greatly improved performance
Available from Sainsbury's (£3.70 pack of four)
Pros
Fantastic all-round performance
Improved new formulation
Con
Shorter lifespan than lithium batteries in higher-drain devices

-------------

Best Buy: Duracell Plus AA
Our score and verdict 75%, A brilliant all-rounder
£4.98
Ryman UK
£4.99
Millets
£5.97
GO Outdoors
£8.00
Pros
Suitable for all types of devices
Widely available
Cons
Not as long lasting as our highest-scoring Best Buys

----------

Best Buy/Great Value: Varta Longlife Power AA
Our score and verdict 73%, Long-lasting alkaline batteries
Available from Battery Station (£1.59 pack of four), BuyaBattery (£1.75 pack of four)
Pros
Solid for energy-guzzlers
Ideal for low-drain devices
Cons
Outperformed by top-rated Best Buys

----------

Lidl are £2 for four and not quite as good at 68%
But at less than half the price, IMO better value.

Aldi at £2.49 for ten scored 54% and are my choice. I'd get Lidl if they do a big pack at that price.

Morrisons were 66% at £3 for four and you can get better for less.

Duracell Optimum scored 56% so not a good Buy.

 

[ericmark]

Ups, done it twice. Really good info. I had to change batteries in my wall thermostat after just 3 weeks, date 10-2027 so likely already 8 years old, as it seems the use by date is 10 to 12 years from manufacturer.

But wall thermostat easy to change, and it sends a note to phone when they are too discharged, so not too worried.

Cat flap is another story, renewed on cat flap as thought faulty, cells not lasting very long, last lot must have lasted at least 9 months, but the problem is we don't see the red LED flashing, and so cats get locked out. So for cat flap cell life is important.

The TRV heads we tend to change every year, so as long as they will last a year, no problem, some seem to last over two years where hard to get to, so not changed.

But a rechargeable cell, AA, some down to 750 mWh and some up to 2400 mWh but they are clearly marked, no guess work, it tells you.

my TRV head actually tells me the voltage, as to what point to change, not so easy, as the graphs show how some batteries have a near parallel line mid use, so can only see when new, or near depleted, but others the graphs show how much energy left. So this

does not really tell me much, as far as time before I need to change.

The Ah it seems very dependent on load

I actually found a test on the cells I know with lead acid we had cold crank rate, Ah @ 10 hour and Ah @ 20 hour rate, so this is nothing new, but with all the TRV heads, looking at around £20 a year just on AA cells. In TRV, wall thermostat, cat flap etc.

 

[JohnD]

I have a number of electricity monitors, all identical. When I remember, I write the battery type and change date on a slip of paper and put it in the battery compartment. I've got two that need changing, they had 2000ma rechargeable AAs fitted two months ago. I looked at another that had Lidl alkaline fitted Sept 2025 and still going strong.

I will see if any others have more dates.

 

[ericmark]

Good idea.

 

[denso13]

last lot must have lasted at least 9 months, but the problem is we don't see the red LED flashing, and so cats get locked out. So for cat flap cell life is important.

Change them every 8 months?

 

[JohnD]

Yes, I found one. All alkaline.

Oldest first
Wilko cheap, 11 months
Energiser, 11 months
Aldi 7 months
Aldi 12 months
Lidl 22 months
Aldi 17 months

Looks like the quality has improved over time.