[Question] Rechargeable Batteries - Li-Ion?

[irneb]

Nearly everything these days (well small portable stuff like cellphones, digital cameras, etc) come wih their own proprietary batteries. Usually the newer ones are Li-Ion, very few are still using the older NiMH, while nearly none are using the extinct NiCd.

Unfortunately, some items use normal penlights (AA) batteries. E.g. Garmin, Olympus, etc. Now you either have a choice of 3 types of batteries:

1. Normal (non-chargeable) alkaline
2. NiMH chargeable
3. "Litium" non-chargeable.

What gives? Why a Lithium which isn't chargeable. Everything else uses Litium Ion chargeables in proprietary batteries.

The reason I'd like to see Li-Ion in AA format is the following: I'm using a Garmin Colorado for tracking during my hiking trips. So I've bought a few sets of AA NiMH batteries - power varying from 1800mAh to 2900mAh. All of them die within 2 days (± 12 hours of use) - some worse than other brands. So going to a normal alkaline "Duracell" - this lasts a whopping 5 days, no recharge though. And then I tried the so-called "Lithium", all I can say is a full 9 days worth, still no recharge .

I've found that this is the case with other stuff as well. Have 2 similar digicams, a Olympus SP-570 and a Lumix FZ18. The Oly uses 2xAA, while the Lumix uses a Panasonic Li-Ion rechargeable. I can take a max of 120 pics using the Oly with 2x NiMH 2900mAh. The Lumix fills up a full 4Gb SD (that's about 1000 pics) and then there's still power for another 200 or so. I can take about 600 on the Oly with Duracells (Haven't tried the Litium bats yet).

Why is there no Li-Ions in AA format. Or for that matter any standard format.

[duncan drennan]

Lithium-ion cells are typically around 3.7V. This is due to the chemistry of the batteries. The electronics for AA batteries will be based around a 1.5V cell. The electronics would have to be changed a bit to allow for the different cell voltages. That is my immediate thought, not sure if there are any other particular reasons though.

[irneb]

Yes, I understand that. Couldn't they then simply make a conductive "dummy" battery so you can place 1x LiIon + dummy to get 3.7V, where the series connected alkaline would give 2x 1.5V = 3.0V: not that much difference.

The alternative NiMH gives a different result: each AA is at 1.2V. I know my father's got an older Pentax digicam and he can't use any NiMH batteries in it at all - voltage to low to operate. He's stuck with alkalines only.

[duncan drennan]

Couldn't they then simply make a conductive "dummy" battery so you can place 1x LiIon + dummy to get 3.7V

That is what I was thinking about quite a bit this morning. There are two issues which would need to be worked around. Firstly, it would probably be wise to regulate the voltage down to 3.0V unless you knew that the electronics were fine with that (lower voltage link NiMH won't break anything, higher voltage might).

The second issue is the question of the physical size of a lithium ion. They are typically flatish rectangular batteries.

I am sure that with a little bit of smarts and an understanding of the physical limitations of the battery holder it would be possible to design something that could be used. It might be a worthwhile project if the design could fit a number of different devices without interfering with the enclosure....

[Loman]

What about a transformer? I'm sure you might be able to get one that can convert 3.7V to 3V. With such a small difference in voltage it won't be very large.

[irneb]

That's probably how they'll do it. However, you'll need a inverter 1st (to change from DC to AC so the transformer will work). Then the transformer. Then a AC-to-DC converter so the output is a steady 3V DC as required.

The major problem here is that you'll need to make it in two parts, or small enough to fit into just one AA size. The 2 parts idea is not that simple, because of the inverter / converter scenario which happens outside the used DC current so it can't just be connected in series. If it was only a transformer, it might have been possible. So until they can make these into smaller components I don't think it's possible.

Doing a quick search on Google I find quite a few of these working into higher voltages (but they're quite bulky as well). However it seems that a Buck Converter might be the way to go.

[duncan drennan]

A transformer requires AC (as irneb has pointed out).

A buck converter is a switching power supply and can be made very small depending on the power requirements. Most portable devices will normally have a buck/boost converter in their power supply. This either raises or lowers the DC voltage (very efficiently) to a suitable operating voltage for the device.

You might want to try rechargeable alkaline batteries. They don't have the same capacity as a NiMH or Li-Ion, but they have a voltage which is the same as a normal AA battery. NiMH are normally 1.2V cells. The power supply inside the device may be sensitive to lower voltages which means the device is turning off, even though the batteries have not yet delivered their full charge.

[Yvonne]

Mini-Solar panel on your hiking hat?

[irneb]

Mini-Solar panel on your hiking hat?

Yes that's probably the only current solution for me. It's not the most ecologically friendly thing for a hiker to do, when he's got a whole bag full of throw-away batteries is it?

Oh well ... down to Cape Union or such to see what they have in a solar recharger.