Ni-Mh batteries

[Twiggy]

Still remember them Ni-Cd and Ni-Mh batteries?

I still remember the Ni-Mh batteries of old days. Very slooooow chargers, lots of energy loss after a short period of non-usage, and stuff.

We're getting spoiled by modern low self-discharge Ni-Mh batteries it seems. I blame eneloop. They're everywhere! And they behave mostly like Li-On batteries! No memory effect, very fast charging even with 2.5 Ah cells, and usable out of the box and even after long periods of storage! Coupled with a smart quick charger you can get said charging times. I thought I'd never see the day where you can charge two Ni-Mh cells in just slightly over 2 hours. Safely.

I got a bundle of 4 AA eneloop XXs and an international "smart" quick charger off a slight discount at the local electronics dept. store.

What do you think of them? Sometimes I feel like that they're not really long for this world, but it came in very handy when you've still got stuff that accepts AA.

[Shade]

I have quite a few actually. Some of those old 2300 mAh AA and 900 mAh AAA batteries Energizer made. I don't know why I keep them, as they don't really hold a charge anymore. Maybe for nostalgia?

A bit off topic, but I find it funny that a single AA has more capacity than a typical cell phone battery.

[Twiggy]

Originally Posted by Shade

I have quite a few actually. Some of those old 2300 mAh AA and 900 mAh AAA batteries Energizer made. I don't know why I keep them, as they don't really hold a charge anymore. Maybe for nostalgia?

A bit off topic, but I find it funny that a single AA has more capacity than a typical cell phone battery.

Alkaline batteries have different maximum capacity depending on the load. Good thing Ni-Mh and lithium stuff don't do that. Has it been a long, long time since the last time you charged the Energizer batteries? (The Ni-Mh batteries I have behave more like Li-On batteries, so no cycling is expected, nor advisable)

Also, the average Ni-Mh battery has the capacity rated for 1.2 V - the average Li-On battery on mobile devices are about 3.6 V or something close. My laptop has a 11.4 V battery with a capacity of 4200 mAh. That doesn't mean that it holds barely any charge (or that my laptop is superefficient). The 4200 mAh in my laptop is basically 13300 mAh in smartphone battery terms. Likewise, the 2500 mAh eneloop XX cells I have are equivalent to 833 mAh in terms of equivalent to 3.6 V, too. :3

I got these batteries because I had something that chews through AA cells like breakfast. >.< It's the Bluetooth mice I bought two weeks ago, and I'm through 4 of them. At 5 V (the rating seems to be given for USB voltage), two of them 2500 mAh (5000 mAh total) eneloop XXs would be about equivalent 1200 mAh (5000 * 1.2 / 5).

I'm actually fine with the fact that my eneloop batteries have only 500 cycles, because I needed the absolute capacity. :3

[Shade]

My cellphone's default battery only has a mAh rating of 1750, compared to the 2300 mAh rating of one AA battery. That was what I was getting at. As for the charge part, the Ni-Mh batteries don't seem to hold a charge anymore.

[Twiggy]

Originally Posted by Shade

My cellphone's default battery only has a mAh rating of 1750, compared to the 2300 mAh rating of one AA battery. That was what I was getting at.

Heh. Shows you that mAh ratings are not comparable without voltage ratings, eh?

Originally Posted by Shade

As for the charge part, the Ni-Mh batteries don't seem to hold a charge anymore.

They're probably well-used at this point, then. Maybe it's time to get a set of low self-discharge Ni-Mhs if you still need to use AAs.

[Cat333Pokémon]

Milliwatt-hours (milliamps × volts × hours) are always the best unit to compare batteries of different voltages. This value tells you how much total juice can be sapped out of the battery and the effective capacity.

How many volts does your phone use? I'm guessing 3.7 volts.

Your cell phone battery: 6,475 mWh
AA battery: 2,600 mWh

Originally Posted by Cat333Pokémon

The average alkaline AA is rated about 2,122 milliamp-hours, while the average AAA is rated about 1,150 milliamp-hours. Given a typical drain of 1.225 volts:

AA: 2.122 Ah * 1.225 V = 2.599 Wh
AAA: 1.150 Ah * 1.225 V = 1.409 Wh

And comparing the watt-hours:

100% * 2.599 Wh / 1.409 Wh - 100% = 84.5%

The typical AA battery has 84.5% greater capacity than the typical AAA battery, assuming identical composition.

For anyone else interested, the ampere-hour ratings on other common alkaline (at "1.5V", 1.225 true volts) cells:
C: 7,800 mAh (9.555 Wh), 554% greater than AAA
D: 17,000 mAh (20.825 Wh), 1100% greater than AAA

[Twiggy]

Heh. I guess it's something very fun to try to compare batteries for different devices with different voltages, eh?