I’ve been going around replacing all the AA and AAA batteries in household implements with rechargeable ones as they expire. All good stuff.

However our smart rad valves take AA and the rechargeables need replacing about every two weeks currently. The old Duracells would last 6 months plus (much longer over summer as far less use).

Now they have to maintain the valve wifi connection plus drive the little motor which opens the valve, so fairly high demand i guess. But thats a huge difference in charge times!

I’ve just noticed the mix of Duracell and morrisons own brand rechargeables are 1.2v rather than 1.5v from the single use cells. Would this affect it? Why are the rechargeables 1.2v not 1.5v? And is there a better option i should be looking at?

What smart valves are you using?

I ask as we have the same problem. We are using Netamo valves.

All the rechargeable batteries we have are 1.2v.
A mix of the panasonic ones and EBL 2800mAh ones.
The ebl ones seem to do really well and last plenty long enough for us. Not tried duracell etc though

Alkaline batteries are above 1,5V when new, dropping gradually in service. Normal rechargeable batteries only give 1,2V, so if the valves are voltage sensitive they will stop working sooner on those.

You need rechargable batteries with slow self discharge. Normal cells discharge themselves and are not suitable for these use cases!

ALDI/LIDL ones are normally the correct ones!

A lot of batteries are fake with appalling performance, try Amazon or IKEA batteries direct from the brands and you know what you’re getting. Lifespan shouldn’t be anything like what you’re getting, I get a year from aa (non rechargeable) on our rads at the moment (hive valves)

Why are the rechargeables 1.2v not 1.5v?

Because the voltage is determined by the cell chemistry. If you want more than 1.2V you need to connect more cells in series, but whatever you do you can’t get 1.5V – just multiples of 1.2V.

My problem is they’re often a bit bigger than normal AAs or AAAs and won’t fit in my torches.

As above normal rechargeable batteries self discharge quite a bit over time. You want the ones that say ‘ready charged’ or ‘pre charged’. These hold onto their charge for ages which is why they are sold as pre charged. They haven’t self discharged in the box.

Eneloop are the business

As above, it’s a result of the diffrent chemistry used to create the leccy charge. There are a few smart things around that son’t work reliably with the lower output

As above normal rechargeable batteries self discharge quite a bit over time. You want the ones that say ‘ready charged’ or ‘pre charged’.

Came here to say this. I always use Eneloops, but anything advertised as pre-charged will be the same technology.

I have TCP valves and they state that rechargeables cannot be used.

As others have said, the slightly lower voltage must be the issue.

Battery capacity with modern NiMH is as good if not better than Alkaline so that’s not usually the problem, nor is discharge not a couple of weeks anyway, so probably voltage. Are ready charged any higher?

I have Wiser smart valves which are known to be incompatible with most rechargeables, seems to be a common thing with smart values, which in this day an age is unforgivable really. I bought a big box of Alkalines just for them.

I use Eneloop Pro (black) in Xbox controllers. Makes my life much easier until I flip my shit that one has disappeared (££££)

Came here to say this. I always use Eneloops, but anything advertised as pre-charged will be the same technology.

They might be the same tech but they’re not as good IME I’ve got quite a few GP and Uniross batteries but Eneloops seem far more reliable over the longer term – I’m not buying anything but them in future.

I think it’s also worth having a decent charger. I’ve got one of these
https://www.batterylogic.co.uk/technoline-bl700n-battery-charger.asp
‘Fast’ chargers are supposed to kill the batteries quicker. However, if a battery is run completely flat I find sometimes that smart charger rejects it, but sticking it in a ‘dumb’ charger for 20 seconds is enough to kickstart it, and the smart charger will work again (but usually worth running a ‘refresh’ cycle on it)>

They might be the same tech but they’re not as good IME I’ve got quite a few GP and Uniross batteries but Eneloops seem far more reliable over the longer term – I’m not buying anything but them in future.

Handy to know, ta.

My problem is they’re often a bit bigger than normal AAs or AAAs and won’t fit in my torches.

This is a problem with the lidl batteries which I have a lot of.

Eneloops though are a similar size to normal alkaline batteries.

Eneloop are the business

Only buy eneloops now.  Saves a lot of pain.  They do eventually need replacing but they seem to last a lot longer and self discharge slower.

We have a load of Tado TRVs which are supposed to run on non-rechargeable batteries; most of ours are fine with rechargeables but a couple aren’t, in some of them the batteries last ages, in others they don’t, it’s all very random.

I’ve just “converted” a battery powered device by using a clever thing that has a couple of dummy batteries and one “battery” that has a wire coming out of it that plugs into the wall. It seems to work very well, to the point I was wondering about whether I could get the TRV that seems to eat batteries to run from the mains instead…

I use 1.5v rechargeable ‘AAs’ similar to these in my RC handset and a couple of games consoles. The voltage drop is very different to a normal akaline, ie these work then will literally fall off a cliff with almost no voltage drop but that’s fine. Normal 1.2 rechargeables don’t work in some of my stuff as the voltage isn’t high enough

EDIT god knows what that kindle error message is! Just go on Amazon and search for 1.5v rechargeable AA and look for the ones with micro usb ports on them

I imagine it is voltage drop, alkaline are meant to hold up then fall off a cliff, as compared to cheaper single use which are more of a slope discharge pattern. Hence lots of electronic stuff says to use alkaline. My grandparents always had a plethora of dim but not dead torches, these days it’s blinding or dead.

When you are giving away 0.3V per cell you are not off to a flying start 🙁

A lithium rechargeable battery should work ok – it solved the problem with our Tado valve batteries reporting issues.

as above, rechargables are 1.2. Just how it is, and these days things are more sensetive.
Ive not seen those super pricey Eneloop ones before. pressumabyl they work ok. they are the same chemistry though.

you can get Lithium Ion batteries in an AA form (the battery will be smaller inside, and it will have an on board controller to manage it, and it will require a special charger)

ive put a “main adaptor” on our cat flap. Its a box of dummy batteries, one of which has a flat ribbon cable coming off it, that plugs into a wall adaptor giving an appropriate voltage. Works perfectly, as long as you can hide the cables to your satisfaction.

alkaline are meant to hold up then fall off a cliff

Not really – they are better than zinc carbon but they still get weak towards the end. Rechargeables have a much flatter voltage curve than Alkaline.

As you can see from this graph, the useful charge of a battery depends on what your minimum required voltage is.

Tado specifically recommend Eneloop batteries (only on V2 hardware though). From memory they have to be the standard rather than ‘Pro’ as the larger capacity were also fractionally larger diameter.

I have 6 Tado TRVs running Eneloops and battery life is several months at least, hardly ever get battery alerts.

IKEA Ladda are also very good (but not for Tado due to size). Made in the same place an Eneloop, allegedly.

Imho:

Rechargeable batteries are supposed to improve with each dis/ charge cycle.

It helps if you can completely discharge your rechargeable batteries, prior to recharging them.

Maybe have an old radio handy, or just slot them into the charger for a week, without it being plugged in.

Lidls recently sold a dinky little charger with a digital display and usb output.
It could power batteries up to 2700mah.

The eight-cell one that ikea sells is quite good, allowing you to mix different Nimh batteries. But with a max capacity of 2450mah, per battery.

If your’re struggling to sleep one night, give this a watch 🙂

It helps if you can completely discharge your rechargeable batteries, prior to recharging them.

one of the good things about that techno line charger is that it has a discharge function which will run them down before charging.

Some great info here, thanks all!

Our valves are Bosch Easycontrol (they’re not easy to control, it took me over a year to understand the nuances of how to get it to do what I wanted).

Just checked the manual, and while it doesn’t specify battery type, it does say they should last 2 years plus! Even the top duracells weren’t close to that!

It also says Imax 120 mA if that has any bearing?

Anyway looks like I’ll try some Eneloops, see if that helps.

It also says Imax 120 mA if that has any bearing?

Is that correct? most AA rechargables are around the 2000mah mark

Different things – 120mA is current delivery, 2000mAh is capacity. So a 2000mAh battery could deliver 120mA for 16 hours.

Eneloop are good, but so are most pre-charged batteries, they mostly got their rep by being early to market, like a schwalbe 650b tyre. I tend to just buy whatever is cheaper on amazon- I’m not convinced my eneloops are any better than my cheap Bonais frinstance. (also seems possible to me that your application has a minimum voltage cutout and that probably the batteries could go further without it? AAs of all types tend to struggle with smarter electronics, since they v-droop more than larger or more modern batteries)

Another option is the little AA sized lipos. These are clever, they have a little voltage controller in so they give a steady 1.5V stepped down from whatever the native voltage is (3.6v?), and for a really long time. They generally charge via a usb in teh side. The downside is that they’re bloody expensive. But they’re a useful thing for when normal rechargables aren’t cutting it

You might be able to bodge it with a lithium chemistry 14500, and either converting the battery box to be parallel, or using a dummy cell. But that’s got very variable results, it’s pretty hard to recommend.

Yeah, Ikea, Energizer, Duracell and amazon seem to all fair fairly well aginst the Eneloops, which seem to be the benchmark.

I have some of these in my rotation and they seem as good as any and better/longer lasting than the duracels I have (but the duracels are rated at lower capacity and I’ve had for longer (they are older/more charging cycles) to be fair).

https://www.ebay.co.uk/itm/401283455055

I use 1.5v rechargeable ‘AAs’ similar to these in my RC handset and a couple of games consoles. The voltage drop is very different to a normal akaline, ie these work then will literally fall off a cliff with almost no voltage drop but that’s fine. Normal 1.2 rechargeables don’t work in some of my stuff as the voltage isn’t high enough

+1

They’re lithium batteries (so 3.7V) with a regulator built in. Hence why they’ll output a rock steady 1.5V right up untill the battery protection kicks in.

It helps if you can completely discharge your rechargeable batteries, prior to recharging them.

sorry but this is just plain wrong. don’t do that.

I’ve been using rechargeables of various brands for decades though i’ve not got smart valves. The eneloops are the ones that i keep buying because they stay charged when not in use and don’t fail provided you don’t absolutely flatten them to the point a smart charger doesn’t recognise them. They do get inadvertently thrown out from time to time but we can’t blame sanyo/panasonic for that.

It helps if you can completely discharge your rechargeable batteries, prior to recharging them.

sorry but this is just plain wrong. don’t do that.

I’m interested to read that @Del. I’d always heard that NiCad or NiMH needed to be completely discharged but you shouldn’t do that with lithium chemistry batteries like LiPo or lithium ion. Is that not right?

I’d always heard that NiCad or NiMH needed to be completely discharged but you shouldn’t do that with lithium chemistry batteries like LiPo or lithium ion. Is that not right?

My memory is that is true for NiCad only, not for NiMh or lithiums.  With NiCad the chemistry allowed for small ‘fingers’ to form internally and eventually short out the battery if it was charged slowly often.  Fully discharging them quickly helped destroy those fingers.  I certainly know that you used to be able to recover some old NiCads by shorting them out but that didn’t work on NiMh and you shouldn’t even try on lithiums

Edit: this article says the opposite, that it is a slow discharge that is needed for NiCads, but is is also for much much larger batteries.it still only applies to NiCads.

Good info, cheers Del and leffeboy 👍.