Apologies for the slightly off topic question but can anyone point me to the best test/comparison of Alkaline batteries vs. the new Lithium rechargeable ones? Older rechargeable AA and AAA batteries were terribly short lived and so mostly useless but I assume Lithium ones are much better?
Lithium isn't rechargable. (Lithium AA cells are very long-life but very expensive. One-time use. Lithium-ion are rechargable, but are 3.7 volts and completely violate the AA spec)
NiMH is the chemistry for rechargable AA / AAA cells, since its 1.35V and "close enough" to the old 1.5V standard alkaline.
> Older rechargeable AA and AAA batteries were terribly short lived and so mostly useless but I assume Lithium ones are much better?
"Older", circa 00s NiMH chemistries had more energy storage (!!!). The issue was that circa 00s cells had a "self-discharge" problem, meaning they ran out of energy in just a few months (like 1 to 3 months).
Panasonic solved the problem with "Low Self Discharge" cells, aka "Eneloop", which started to come out in the late 00s. This chemistry had much less capacity, but took over a year before the energy went bad.
Its still NiMH chemistry, but just tweaked to focus on the self-discharge problem rather than energy-storage numbers / benchmarks.
With Eneloop taking the market by storm (especially popular with XBox users, which used AA rechargables), other companies also came out with LSD chemistries. These days, almost everything you'll find is of the LSD-type.
You can get lithium ion rechargable AA batteries these days. They have a built in regulator to drop the voltage to 1.5V. Some of them even have micro usb ports on the side for charging.
I've not seen AA or AAA sized lithium rechargeable batteries but modern low-self-discharge NiMH AA and AAA cell batteries are quite good today. The Panasonic Eneloop brand are generally widely available and good value for money. The AA size Eneloops are generally around 2100mAh and the AAA size around 900mAh.
The only downside to modern NiMH batteries today seems to be finding a good and easy to use charger which will properly discharge and/or cycle the batteries without requiring a human to fiddle with it or understand charge rates and when to discharge the cell prior to charging.
> The only downside to modern NiMH batteries today seems to be finding a good and easy to use charger which will properly discharge and/or cycle the batteries without requiring a human to fiddle with it or understand charge rates and when to discharge the cell prior to charging.
Only if you're really babying your NiMH cells is it worthwhile to do this.
-----
Frankly, my recommendation is to just throw away NiMH cells once they "go bad" (maybe a discharge/recharge cycle will save them, but they're really not that expensive).
For most consumers out there, the $10 trickle charge that takes 8+ hours is superior, because they'll never cycle the NiMH cells to death. How many dozens of charge/recharge cycles do you need before there's an issue, even with the most primitive of charging strategies?
When it takes months for a typical AA powered appliance to run out of NiMH charge, you realize that these "dozens" of charge/discharge cycles gives a life-span measured in _YEARS_ for these NiMH cells.
After 5 years, your NiMH cells might be on its last legs, needing a full discharge/recharge to get back to full power. Then and only then should you consider a $30 charger to perform this resurrection, except its probably more cost-efficient to just spend $2 and throw away the "old" cell.
You'll need to throw away $20 worth of cells (ie: 10 cells) before your $30 fancy charger with discharge/recharge cycles + coulomb counting is superior to the $10 crap trickle charger. Maybe an RC-car enthusiast will get there (or an electronic-hobbyist), but that's a _LOT_ of charge/recharge cycles before you reach this point. Even with the inferior $10 trickle charge design.
-------
EDIT: That being said, spending $30, $40, or $50 on a higher-end charger because you find it "cool" is probably worthwhile. Coolness is a factor and we're not really talking about a lot of money here. But the $10 charger + buy new cells as needed approach is probably the most cost-effective strategy.
The thing I like about the $30 charger is that it will do a discharge test and tell you how many mAh of capacity the battery has -- much better than having to figure out which battery is bad by rotating them through your bike light until you isolate the bad one.
I believe one other argument for recargeables is that you produce less junk when using them. From that view, just throwing away "bad" but potentially resurrectable cells may not be ok.
There are AA and AAA sized lithium ion rechargables, but they won't work in anything that uses alkalines, since they provide a very different voltage (3.7V). They are usually called 10440 (AAA-sized) and 14500 (AA-sized).
There are AA and AAA lithium _primary_ batteries that provide 1.5V and are in stores, but they cannot be recharged. They are far superior than alkalines in most ways, especially in the cold, but they cost drastically more, around $1-2 each. I've switched many of my low-drain applications to these batteries, where they are likely to outlast the device without leaking and destroying it.
Note the small link near the top titled "Comparator" if you want to generate comparison graphs between different batteries.
1.5V Li-ion rechargeable AAs are 3.7V cells with DC-DC buck converters attached to reduce the voltage. The main reason to use them is poorly-designed[0] devices that don't play well with NiMH. There may be some standby power drain from the electronics, and these are less compatible with voltage-based battery status monitoring than NiMH (NiMH gives a false low reading; bucked Li-ion gives a constant false full reading).
Modern low-self-discharge NiMH has very good performance and shelf-life; the white Panasonic Eneloop is the gold standard in this category; the black ones have higher capacity, but wear out in fewer charge cycles.
[0] Even if designing for alkaline without NiMH support isn't a design flaw per se, a device that doesn't work at 1.2V leaves about half the energy stored in an alkaline unused.
I've been a bit puzzled by the 1.5 V lithium AA batteries I see on Amazon. They say they are a constant 1.5 V all the way from 100% charged to 0% charged.
With the battery presenting a constant voltage, wouldn't that make battery level displays useless? They rely on the voltage declining as the battery discharges. With a constant 1.5 V battery your device is going to say the battery is full right up until it suddenly stops.
The AA lithium-ion rechargeable are internally 3.7V, just like any other lithium-ion battery. They have a buck converter build-in that regulates that down to a constant 1.5V. Which can be handy in the handful of applications that don't deal with the 1.2V that NiMH provide. This does in turn make battery indicators indeed completely useless for many of them, as there is no detectable drop in voltage from the outside of the battery.
However, there are newer ones take care of that and regulate the voltage down to 1.1V or so shortly before they run completely out of juice, so that the battery indicator can give a warning. Don't know how widespread that feature is yet, but it exists.
That's Energizer's Lithium of course, but you can expect that competitors probably perform "similarly".
------
You can see that Energizer Lithium is 1.7V, slightly more than the 1.5V found in typical Alkaline cells. Today's electronics are pretty flexible however, and this may not be an issue. (In practice, AA-devices are usually designed for 1.35V NiMH, 1.5V Alkaline, and 1.7V... but there are some devices that have made 1.5V assumptions and _ONLY_ work with Alkaline)
