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Using NiMH rechargeable batteries


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I'm trying out a set of NiMH batteries and would like to find out if what I experience is normal.

 

Firstly, I noticed that the batteries are rated at 1.2v 1800mAH

 

When fully charged and installed into my Etrex, the setup page shows tha battery indicator to be about a third to three quarters full (due to the lower voltage ? )

 

Has anyone been using NiMH rechargeables over a long period ?

Would like to know if the above is normal and how long these things last. From what I see looks like I may need to bring several spare sets with me just in case.

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quote:
Firstly, I noticed that the batteries are rated at 1.2v 1800mAH

 

That's what it's all about, normal non-rechargeable batteries are rated 1.5v. This is why the indicater never shows full with the NiMH.

 

I've been using NiMH in my Vista for about a year now without any problems. Of course Duracell's last longer but the overall cost is a lot higher than using rechargeable batteries.

 

When geocaching I usually carry 2 sets of spare batteries, one set NiMH and one set of brand new Duracell's (never needed these yet).

 

"Yo no busco..., encuentro" (Pablo Picasso)

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A typical alkaline AA cell has about a 2200 mAh capacity, so your 1800 mAh cells will have about 80% of the capacity of alkaline cells per charge, assuming they are fully charged. So if alkaline cells will power your GPS for 15 hours, then the NiMH will go about 12 hours per charge. If the battery indicator is set for alkaline cells, it will read about 80% or 90% on fully charged NiMH cells. As the NiMH cells discharge, the indicator will drop off to the 70% range within an hour or so and then go slowly down to about 30%. The last 30% of the indicated capacity will go really fast, so fast that you may not even get a low battery indication. Another good thing to know is that NiMH cells will slowly discharge after a full charge, about 2% to 4% a day. So it does not work too well to charge the cells more than a week before you use them. Typical NiMH cells are good for about 300 charge cycles or 3 to 4 years, whichever comes first.

 

FWIW,

CharlieP

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quote:
Originally posted by CharlieP:

A typical alkaline AA cell has about a 2200 mAh capacity, so your 1800 mAh cells will have about 80% of the capacity of alkaline cells per charge, assuming they are fully charged. So if alkaline cells will power your GPS for 15 hours, then the NiMH will go about 12 hours per charge. FWIW,

CharlieP


 

In digital devices, it does not work this way. Your understanding of battery capacity would apply to flashlights - not GPSrs. Typically, you get longer life from the above battery examples with the NIMH, not the alkaline.

 

MajBach

You can't have everything,where would you put it?

1compass.gif

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quote:
Originally posted by MajBach:

quote:
Originally posted by CharlieP:

A typical alkaline AA cell has about a 2200 mAh capacity, so your 1800 mAh cells will have about 80% of the capacity of alkaline cells per charge, assuming they are fully charged. So if alkaline cells will power your GPS for 15 hours, then the NiMH will go about 12 hours per charge. FWIW,

CharlieP


 

In digital devices, it does not work this way. Your understanding of battery capacity would apply to flashlights - not GPSrs. Typically, you get longer life from the above battery examples with the NIMH, not the alkaline.


 

Actually, he IS right. You are correct with high drain digital devices, such as digital cameras. The internal resistance of alkalines is so great, you can kill an alkaline battery with less than a dozen shots off a digital camera, and 2-3x that amount with Lithium, NiCAD or NiMH (which all have much less internal resistance). Most of the current flow in the alkalines is turned into heat instead of useful work.

 

On low-current devices, alkalines are best for longer life-- but a set of NiHM in my Vista and one in my fanny pack will last nearly 24 hours of straight use, more than enough for my needs as a much lower cost than alkalines.

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I have made some measurements of battery life with an eTrex Venture, see http://opentopic.Groundspeak.com/0/OpenTopic?a=tpc&s=1750973553&f=5740990093&m=4910905034

 

I also want to share what I have learned about the capacity and voltage ratings for alkalines and NiMh The 1,5V in alkalines and the 1,2V in NiMh is not comparable. For alkalines 1,5 volts is the open-circuit voltage (The no load voltage of a cell or battery measured with a high resistance voltmeter), that means no current drain. That is not the whole truth, an unused alkaline has a open-circuit voltage of 1,6V but that soon drops to 1,5V. If you measure the open-circuit voltage on a fully charged NiMh directly off the charger the open-circuit voltage is almost 1,4V. The open-circuit voltage is the above 1,2V until it's discharged. But we have no use of the open-circuit voltage. We use the batteries to power all out gadgets. If you plot the closed-circuit voltage (Voltage as measured of a cell or battery under a specific discharge load and time interval) versus discharge time there are big differences. This discharge characteristics are very different for alkalines and NiMh. I found some illustrative diagrams on Energizers website. Take a look at http://data.energizer.com/datasheets/library/primary/alkaline/energizer/consumer_oem/e91.pdf for alkalines and http://data.energizer.com/datasheets/library/rechargeables/consumer/nimh/nh15.pdf for NiMh.

 

The first thing to observe is that the rated capacity is defined at different rating drain. The NiMh is rated to 1700mAh at 340mA current drain and 1.0V cut off, the alkalines to 2850mAh at 25mA current drain and 0.8V cut off. The capacity for the alkalines at 340mA current drain and 1.0V cut off is only 1350 mAh (from the diagram "Constant Current Discharge Typical Service). The eTrex shuts down at 2.0V, that is 1.0V/battery.

 

The next thing is that the discharge diagrams looks different. For the NiMh the closed-circuit voltage drops to just below 1,3V and thea stays there to the end of the discharge when it drops fast. (at 170mA current drain, close to an eTrex). 1,2V closed-circuit voltage is not reached until after 90% of the capacity is used. For the alkalines 1.3V is reached after 15% and 1,2V closed-circuit voltage is reached after 50% (according to the diagram "3,9 ohm 1 hour / day" and 1,0V cut off) of the capacity is used. This means that during most of the time the NiMh has a higher closed-circuit voltage than the alkalines!

 

This is why the NiMh works so good in our GPSr's despite the 1.2V rating. In low temperatuers it gets even worse for the alkalines. All this is also consistent with the results of my own measurements.

 

The discharge diagrams also explains the behaviour of the battery indicator in the eTrex (and others I believe).

 

"Qui quairit invenit"

/Morgan Geocacher and MinuteWarrior

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quote:
Originally posted by rworne:

 

Actually, he IS right. You are correct with high drain digital devices, such as digital cameras. The internal resistance of alkalines is so great, you can kill an alkaline battery with less than a dozen shots off a digital camera, and 2-3x that amount with Lithium, NiCAD or NiMH (which all have much less internal resistance). Most of the current flow in the alkalines is turned into heat instead of useful work.

 

On low-current devices, alkalines are best for longer life-- but a set of NiHM in my Vista and one in my fanny pack will last nearly 24 hours of straight use, more than enough for my needs as a much lower cost than alkalines.


 

Many, if not most digital devices are high drain. Most GPSr witha draw of around 300 mA would fall into this category. Even if they were not high drain, they still require 1.1 V or more to operate. At that voltage, alkalines cannot supply 300 mA, unlike NiCd or NiMH.

 

MajBach

You can't have everything,where would you put it?

1compass.gif

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quote:
Originally posted by MajBach:

 

In digital devices, it does not work this way. Your understanding of battery capacity would apply to flashlights - not GPSrs. Typically, you get longer life from the above battery examples with the NIMH, not the alkaline.


 

MiMH batteries will outlast alkalines in some high current draw digital devices, e.g. digital cameras. But a GPSR has a relatively low current draw, actually *less* than a typical AA flashlight. Therefore, the alkalines will outlast the NiMH in a GPSR, and "my understanding" applies to both devices.

 

FWIW,

CharlieP

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quote:
Originally posted by MajBach:

 

Many, if not most digital devices are high drain. Most GPSr witha draw of around 300 mA would fall into this category. Even if they were not high drain, they still require 1.1 V or more to operate. At that voltage, alkalines cannot supply 300 mA, unlike NiCd or NiMH.


 

I strongly disagree. Most GPSR's draw *much* less current than 300 mA. I have tested my Garmin GPS76 and it draws 115 mA in normal mode, 180 mA with the light on. FYI, a small AA flashlight will draw about 200 mA. If our GPSR's drew 300 mA, like a digital camera, then they would only operate a few hours, at most, on alkalines. Most modern GPSR's operate more than 10 hours on alkalines.

 

FWIW,

CharlieP

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I haven't plotted anything, but my experience has been that running NiMH in my Garmin Legend shows the battery indicator to start off about half, but even as it goes to zero the GPS just stays on a lot longer. I tend to get 8 or so hours out of my 1800ma NiMH vs. 6 or 7 hours out of a set of Duracells.

 

I absolutely concur about temperature. As a snowmobiler if I can only get 3 or 4 hours out of a set of alkalines. Leaving my unit on a windscreen mount in 20 degree weather just kills alkalines. NiMH seem to still hang closer to 8 hours in the cold.

 

I do notice that if I don't use a freshly charged set of NiMH that they discharge some over the course of a couple of weeks.

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I have a GPS V and have used both Alkaline and NiMH (1600mah). For average use I got 19hours out of the Alkaline and 10 hours out of the NiMH. The Alkaline's last substantially longer in my GPS. I use them as my backup and run NiMH's since they last me a day of Geocaching before needing recharged.

 

Reports and drainage studies aside that's what I measued with the battery timer on my GPS V. I am looking forward to some 1800mah's.

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Renegade Knight:

 

That number seems low for 1600's. are you running WAAS all the time? I was getting right at 15-16 hours out of my 1600s, averaged over several runs (no waas on). If you only have one set you might have a marginal or defective cell...

I have gotten 10 hours with 3 hours of waas use and 4 hours of backlighting thrown into the mix

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I have a Garmin eMap and have used alkaline, NiCad, and NiMH batteries in it. Alkalines last about 10-12 hours. The NiCads and NiMHs last about 2 hours if I recharge them immediately before I use them...otherwise maybe 1 hour or less. I gave up even using rechargables. This usage time has been verified in the field over and over again. I have been very disenchanted with my rechargeable batteries.

Mike Landis

victorymike

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nicad, lithion, alkaline, you name it these are all dangerous chemical containing batteries... not while there on your shelf or in use but years later after they are decomposing. Please either recycle these (best buy etc...) or look up to find your local household hazardous waste collection day. My city collects it 2 times a year along with any other nasty chemicals (paints solvents etc.). These batteries are regulated by the EPA. If you were a buisness and you throw them away, your violating federal law (RCRA) and probably state laws (Universal Waste Rules). Please be responsible!! Recycle your hazardous wastes!

 

Coincidentally, alkalines are broken down into potassium salts by several recyclers and the potassium salt is sold to animal feed manufacturers. Interesting huh?

 

. . . . . ..T 3 a |/| B a || d i T 0.. . . .

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nicad, lithion, alkaline, you name it these are all dangerous chemical containing batteries... not while there on your shelf or in use but years later after they are decomposing. Please either recycle these (best buy etc...) or look up to find your local household hazardous waste collection day. My city collects it 2 times a year along with any other nasty chemicals (paints solvents etc.). These batteries are regulated by the EPA. If you were a buisness and you throw them away, your violating federal law (RCRA) and probably state laws (Universal Waste Rules). Please be responsible!! Recycle your hazardous wastes!

 

Coincidentally, alkalines are broken down into potassium salts by several recyclers and the potassium salt is sold to animal feed manufacturers. Interesting huh? icon_biggrin.gificon_biggrin.gificon_biggrin.gif

 

. . . . . ..T 3 a |/| B a || d i T 0.. . . .

Link to comment

nicad, lithion, alkaline, you name it these are all dangerous chemical containing batteries... not while there on your shelf or in use but years later after they are decomposing. Please either recycle these (best buy etc...) or look up to find your local household hazardous waste collection day. My city collects it 2 times a year along with any other nasty chemicals (paints solvents etc.). These batteries are regulated by the EPA. If you were a buisness and you throw them away, your violating federal law (RCRA) and probably state laws (Universal Waste Rules). Please be responsible!! Recycle your hazardous wastes!

 

Coincidentally, alkalines are broken down into potassium salts by several recyclers and the potassium salt is sold to animal feed manufacturers. Interesting huh? icon_biggrin.gificon_biggrin.gificon_biggrin.gif

 

. . . . . ..T 3 a |/| B a || d i T 0.. . . .

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quote:
Originally posted by victorymike:

I have a Garmin eMap and have used alkaline, NiCad, and NiMH batteries in it. Alkalines last about 10-12 hours. The NiCads and NiMHs last about 2 hours if I recharge them immediately before I use them.


 

Something is wrong with either your eMap or your rechargable batteries. My eMap operates for about 6-7 hours per charge on NiCd cells and 11-12 hours per charge on NiMH.

Maybe yours is shutting down at too high a voltage level and therefore leaving much of the potential energy in the rechargable cells unused.

If it's still under warranty I would suggest checking with Garmin and seeing if they'll fix/replace it.

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quote:
Originally posted by Vertigo:

Yeah but can you charge your alkalines in one hour? Can you use them more than once?

 

Longest life actually should come from a set of lithium batteries if everyone wants to get nit picky about it icon_smile.gif


 

Actually, lithium won't give you any advantage if it is a low-drain device. Lithium's main advantage is the low resistance, much like the NiMH batteries mentioned earlier. You won't get the 2x-3x the opertaing time on Lithium than you will off of alkaline.

 

My Vista goes about 10 or so hours on NiMH, and in excess of 13 hours on alkaline.

 

There are many studies about drain vs. battery life on the net. Look some up and compare NiMH, Alkaline and Lithium (disposable) on a low drain device like a GPS at ~ 150mA. You cannot divide the capacity of the battery by the drain and get the operating time, there's other factors to consider.

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quote:
Originally posted by Vertigo:

Yeah but can you charge your alkalines in one hour? Can you use them more than once?

 

Longest life actually should come from a set of lithium batteries if everyone wants to get nit picky about it icon_smile.gif


 

Actually, lithium won't give you any advantage if it is a low-drain device. Lithium's main advantage is the low resistance, much like the NiMH batteries mentioned earlier. You won't get the 2x-3x the opertaing time on Lithium than you will off of alkaline.

 

My Vista goes about 10 or so hours on NiMH, and in excess of 13 hours on alkaline.

 

There are many studies about drain vs. battery life on the net. Look some up and compare NiMH, Alkaline and Lithium (disposable) on a low drain device like a GPS at ~ 150mA. You cannot divide the capacity of the battery by the drain and get the operating time, there's other factors to consider.

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Seems like there are two schools of thought concerning use of NiMH and their lifespan compared to Alkalines.

 

Here's my own results, though not exactly scientific,

 

I put in a set of freshly charged 1800Ah NiMh batteries into my Etrex Summit, then left it indoors with no signal and waited for it to drain. The result : about 7+ hours

 

Yet to try it with alkalines 'cos I stopped buying them once I got the rechargeables.

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quote:
Originally posted by CountryLover:

Seems like there are two schools of thought concerning use of NiMH and their lifespan compared to Alkalines.

 

Here's my own results, though not exactly scientific,

 

I put in a set of freshly charged 1800Ah NiMh batteries into my Etrex Summit, then left it indoors with no signal and waited for it to drain. The result : about 7+ hours

 

Yet to try it with alkalines 'cos I stopped buying them once I got the rechargeables.


When I read the responses here from people stating their NiMH do not deliver as much time on a charge as alkalines, I think to myself: there must be something wrong.

Your NiMH batteries may be well into their service life and cannot hold a full charge relative to brand new. Perhaps they're not fully charged from thr charger. Or, your GPS is one of the few that are really energy efficient and can suck the juice from the alkalines to a much lower voltage.

I wish I still had the link, but some time ago I read a comparison test of the current draw of many GPSrs. My GPSr (GM100) had the highest current draw of them all. There was a Garmin, possibly the V or III+, that came a pretty close second. I just purchased 4 1800mAh NImh. On a full charge, I get 9 - 10 hours of use out of them. Alkalines yield 6 - 9 hours; six if I leave the unit on and 9 if I drain them over several days. Seeing that others are not getting anywhere near the same life from the same batteries in a unit that draws less power than mine, leads me to believe there are something wrong with the batteries state of charge. I don't argue that Alkalines can deliver charge for longer in *some* units, but I do question the observation that 1800 NiMH are only delivering 7 hours. Perhaps this GPSr only requires two batteries?

If you have a lot of time on your hands,

this link is the most informative of all battery links I have read.

 

MajBach

You can't have everything,where would you put it?

1compass.gif

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Just an idea, but i read you all compairing same model battery usage and being conflicted by conflicting reports of varying battery endurance. Well I only use alkaline becasue they recycle the best, (into animal feed) and they are easy to recycle... however you all need to make sure that your compairing apples to apples or vista to vista.. what i mean is that with certain features (WAAS, battery saver, compass) either on or off, my battery life is significantly altered, DUH! well when your all stOOpified that one persons model lasts longer than someone elses same model with same batterys... make sure you divuldge all settings!!

 

Batteries are Universal Waste (a class of Haz waste designated by the federal EPA) link for more info

 

<-T 3 a |/| B a || d i T 0->

S [] U T |-| 3 U < |_ i D [] |-| | []

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