Why do rechargeable batteries deplete so quickly compared to non-rechargeable?

Question

I'm trying to use rechargeable batteries wherever I can, but I have to say that it is quite annoying having to change batteries so often compared to non-rechargeable.

Taking low-drain things like a TV remote control or temperature sensor as an example - I get maybe half a year from regular batteries or maybe a year before having to change them. I don't even know because you pretty much forget about these things. With rechargeable batteries I have to recharge them every 1-2 month or so.

1. Besides all the marketing fluff - are there "better" rechargeable batteries for these low-drain scenarios, e.g. Eneloop? Better: keeping their charge longer.
2. I like using cheap 800mAh AAA for e.g. temperature sensors. I also have 1100mAh AAA or even 2700mAh AA rechargeable batteries lying around. For high-drain things (e.g. camera flash light) I like using the batteries with higher capacity - but is there a benefit in using these for the TV remote? Do they last longer?
3. If there are differences between all these rechargeable battery types, is there a golden rule? E.g. use Eneloop for TV remotes, use high-mAh for flashlights?

Answer 1

Besides all the marketing fluff - are there "better" rechargeable batteries for these low-drain scenarios, e.g. Eneloop? Better: keeping their charge longer.

Yes. Cheap NiMH batteries generally have high leakage and go flat within a few months. LSD (Low Self Discharge) batteries such as Eneloop may hold 90% charge in 1 year and 70% after 5 years.

I use Eneloops in all my devices, including electric clocks and instruments that are rarely used. They recharge in about 1.5 hours, but I keep a few charged spares on hand so I don't have to wait. I prefer this to buying 'dry' cells even though they may last longer in low drain applications, because:-

1. Having to make a special trip to town just to buy a battery is a pain.

2. They are much more expensive when total usage is considered.

3. They are usually sold in packs with more than I need, but perhaps not enough to make a complete set (and then I have to buy another pack just to get 1 more cell!).

4. You never know how much charge they actually have.

is there a benefit in using these for the TV remote? Do they last longer?

Theoretically an Alkaline (not 'Zinc-Carbon') cell should last longer than LSD in very low drain applications. But there may not be that much in it. At lygate-info.dk some batteries were tested at low current drain. A Duracell Plus Power AA discharged at 5 mA to 1.2 V got 2313 mAh, while an Eneloop 3UTGA AA got 1787 mAh, so the Alkaline only lasted 30% longer. But that was a top quality brand. Cheap Alkalines have no stated capacity and cannot be expected to last as long.

The big problem with primary cells is that you have to destroy them to measure capacity, so you never know what an individual cell is capable of until after it is used up. Cheap brands are likely to have lower capacity in general, but also more 'duds' that cannot be weeded out in testing. So you have to accept that those 'new' cells you just put into a device may not last as long as you expect.

Another reason for using rechargables is that 'dry' cells have a tendency to leak corrosive liquid when fully discharged, which can destroy the device they are in. This often occurs in devices which normally run on mains power, as the forgotten dry cells eventually go flat and leak even though they were never used.

Answer 2

The full chemistry-level explanation is beyond me, but the short consumer-level answer is to do with self-discharge. This is, as the name suggests, how much the battery discharges itself while not in use or in low-drain uses.

Some rechargeable batteries are marketed as "low self discharge" for these use cases. However, personally I wouldn't bother using rechargeables for anything with a life over six months because they have a finite shelf life anyway and are unlikely to see enough cycles to justify the extra cost.

Answer 3

One possible reason is at the chemistries of rechargeable batteries yield a different voltage range from non-rechargeable ones, usually lower.

An alkaline (non-rechargeable) battery has a nominal voltage of 1.5V. It will start at 1.59V at 100% and drop to 1.20V at 10% (with zero load, it will be lower with higher loads).

An NiCd or NiMH (rechargeable) battery has a nominal voltage of 1.2V. NiMH batteries will start at 1.4V and drop to 1.1V. NiCd are more stable around 1.2V.

If your device needs a minimum of 1.3V for instance, NiMH batteries will reach that threshold quicker than alkaline.

Also, their chemistries yield a much lower capacity. Rechargeable batteries often have a capacity that is half or even a third of their alkaline equivalents.

Different uses, different characteristics. There has to be a drawback to rechargeable batteries, otherwise the non-rechargeable ones would no longer exist.

Answer 4

The reason why Dry Cells / Alkalines hold their charge as long as they do, is that the ions, atoms in the electrolyte paste, have to migrate very slowly to the Cathode & Anodes over time. Whereas a rechargeable, you're looking at 'leakage' via an invisible magnetic field between the +/-. The stronger the field, the faster the leakage. Both types have a magnetic field between the +/-. In theory.