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gcrank1
Member
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# Posted: 18 Mar 2021 13:31
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I was just seeing some info on small batteries, the old std sizes in HD or Alky are rated at 1.5v but no wonder I was disappointed with the rechargeable versions, they are only 1.2. Here I thought they just 'took a set' and wouldnt charge any higher after a short while and they didnt last very long after a charge. Of course not only starting at 1.2  . Not so good for voltage sensitive devices (flashlights dont much care but do go to dim-bulb; still better than a candle).
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ICC
Member
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# Posted: 18 Mar 2021 18:40
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For most devices the rated voltage difference between alkaline and NiMH is not relevanyt. Most devices will work fine on NIMH, some even work better as NiMH are better at delivering high current.
Devices that constantly draw small amounts of power often work better on disposables; things like wall clocks. I have noted that my clocks do not like NiMH. After a month they don't keep time well on NIMH but will run over a year on an alkaline. One would think that something that draws so little power would work okay on NiMH.
The voltage of an alkaline cell drops much faster than a NiMH and will soon be down to 1.3, 1.2. The NiMH are more like Li-ion in that respect. the NIMH and Li-ion hold a slowly dropping, more nearly constant voltage for a long time.
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DryCreek
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# Posted: 19 Mar 2021 20:55
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"they didnt last very long after a charge"
Just FWIW, there are two flavors of NiMH AA's. Both are rechargeable, but one flavor will self-discharge in a short time, IMHE as short as a few days. They are only useful if, maybe, you have something that uses a set in a matter of hours and you charge them right before use.
The other kind are 'Low Self Discharge'. 'Eneloop' brand are the originals, but there are other brands now. These will still have 70% of their charge after 5 years or something like that.
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Brettny
Member
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# Posted: 20 Mar 2021 07:40
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For sensitive stuff it dosnt matter the brand, starting at 1.2v when they need 1.5v is loosing quite a bit of power right off the bat. Then is your useing them in the cold you loose more.
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DryCreek
Member
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# Posted: 20 Mar 2021 10:50
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"starting at 1.2v when they need 1.5v is loosing quite a bit of power right off the bat"
Not really. It's actually a complicated question that depends on the amperage being drawn from the battery. In general, higher draws favor NiMH. For example, scroll down this to the graph labeled 'Alkaline and NiMH AA Cells - 500 mA Load':
https://www.eznec.com/Amateur/1.5_vs_1.2_Volt_Batteries.pdf
For that load (which is a fairly large load for a lot of things you's want an AA to do), NiMH handily beats alkaline. Unfortunately, that fellow doesn't give the graph for lower amperages. And this source doesn't give the curves, but does have a chart for total watt hours. If you look at the AA chart, he says NiMH have 97% the watt hours of alkaline, which is what I would expect at very low amperages, like a clock or something:
https://www.allaboutbatteries.com/energy-tables.html
And all that is just looking at the batteries, not the peculiarities of the device they are in.
For one example, many modern LED flashlights/headlamps don't just connect the batteries to the LED. In fact, if it only uses one AA, it can't just connect the battery to the LED, because LEDs won't operate at all at 1.5 volts. You need circuitry that boosts the battery voltage to 3.X volts or so (depending on the particular LED). So those kinds of devices don't really care what the battery voltage is, they are boosting it to the voltage they need regardless.
For an example from the other side of the equation, we have one of those wireless driveway alarms. It beeps when it thinks the batteries are low, and the voltage at which it decides to start beeping is pretty high. If you use 4 NiMH rechargeables, it starts beeping 2 weeks later at 2 in the morning, which I don't like. What I did was convert it to use 5 AA's, because 5*1.2 equals 4*1.5, and then it runs happily for months on the 5 rechargeables.
While there are the odd exceptions, in general you will get similar performance from eneloops and alkaline batteries.
Also eneloops won't leak and ruin whatever they are in, and for something like a flashlight you don't have to think 'these batteries are half used, I don't want to be walking in the dark, I better swap in fresh batteries'. You just charge the half used ones and you are good to go.
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paulz
Member
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# Posted: 21 Mar 2021 10:46
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I put my new, freshly charged batteries in a led flashlight earlier this week, used it only briefly so far but pulled them out this morning, still reading 1.35v. I'll check again after I use it more.
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cristy
Member
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# Posted: 20 Oct 2021 02:09
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I had converted to reachable AAs, which I now primarily use. Except for the spy camera, all of my other cameras operate well with lithium.
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