Battery Experts - Why did PocketPC manufacturers do this?

joohang

Lifer
Oct 22, 2000
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Hi all,

I've been looking into expanding the limited battery life of my iPAQ and looked through some commercially available products out there.

I'm heading to downtown RadioShack (the one near my house went out of stock :() to buy this which will up to recharge 4x NiMH and also serve as a DC power source.

According to this article, each NiMH battery (AA, I think) supplies 1100~2300 mAh.

According to the iPAQ specs at Compaq, my iPAQ's Li Polymer battery capacity is only 950 mAh.

Now, I am puzzled why Compaq chose to do this. Doesn't it make more sense to go with NiMH as iPAQ's main battery and perhaps make it AA replaceable?

So what are some possible reasons that Compaq (and other PocketPC manufacturers) chose to do this?
 

joohang

Lifer
Oct 22, 2000
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Originally posted by: Gunbuster
You can mold a Li Polymer battery to fit small odd shapes

But not NiMH?

The only reasons I can think of are that NiMH are heavier and AA/AAA will make the iPAQ too thick. But considering how thick the iPAQ gets with the sleeves, I'd actually prefer a device that lasts longer with easily obtainable and replaceable batteries.
 

joohang

Lifer
Oct 22, 2000
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Originally posted by: mcveigh
I think NiMH are easier to make and cheaper as well.

They go for 11 bucks at Walmart.

In comparison, most Li Ion batteries (for replaceable PocketPCs) cost around $100.
 

zephyrprime

Diamond Member
Feb 18, 2001
7,512
2
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The most powerful AA nimh currently available is 1800mah.

You are missing a critical piece of information with regards to compaq's choice of batteries. Lithium ion & lithium polymer cells are higher voltage than nimh. All nimh cells are 1.2V while lithium ion cells are around 3.6V. The total energy in a battery or cell depends on both it's current rating (mAh) and it's voltage. The forumula for total energy from a battery is: mAh/1000 * 3600secs/hr * voltage = energy in joules

So compaq did not make an illogical choice. Lithium Ion polymer has a higher volumetric and weight based energy density.

Also, as Gunbuster said, you can mold lithium polymer batteries to funny shapes. This cannot be done with any other batter type.
 

joohang

Lifer
Oct 22, 2000
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The iPAQ is actually powered by a 5V battery, although I believe that it will drop to somewhere around 3V at after draining around 70~80% of full capacity.

I understand that NiMH is 1.2V but wouldn't I get 4.8V if I add 4 AA NiMH batteries together (in serial?)? And Walmart sells 4x 1600 mAh batteries for 11 bucks. Would that give me a potential of 6400 mAh?

I see that weight, shape, efficiency and capacity per weight makes the use of Li Ion/Polymer batteries a logical choice. Now I wonder why none of the PocketPC manufacturers thought about designing their devices somewhat like how Palm did. Just have a backup battery and allow users to pop in 4x 1.2V NiMH batteries.

Edit - suck at multiplying today :)
 

kgraeme

Diamond Member
Sep 5, 2000
3,536
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Originally posted by: joohang
Now I wonder why none of the PocketPC manufacturers thought about designing their devices somewhat like how Palm did. Just have a backup battery and allow users to pop in 4x 1.2V NiMH batteries.

Actually, the Jornada does pretty much that. It has a little backup battery that lets you hot-swap the main battery. It's still Li-Ion, but it's slick. Unfortunately, the HP/Compaq merger killed the Jornada line. It's too bad that the iPAQ was the more popular product because the Jornada was actually a better design.
 

RemyCanad

Golden Member
Sep 28, 2001
1,849
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What iPaq do you have? The newer ones have a substantial increase in battery life.
 

joohang

Lifer
Oct 22, 2000
12,340
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Originally posted by: RemyCanad
What iPaq do you have? The newer ones have a substantial increase in battery life.

I am aware of that.

I got a 3635. If I were to replace my iPAQ today, I'd get the Toshiba e740. :D I tried it at FutureShop the other day and totally fell in love with it. :)
 

joohang

Lifer
Oct 22, 2000
12,340
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I just got back from RadioShack and am recharing the 4 AA NiMH batteries as I speak. They are rated at 1600 mAh each for up to 1000 recharges.

The idea is to use this device to serve as a portable DC power source. So the iPAQ will think that the power adapter is hooked up, so it will power itself while recharging the built-in Li Polymer battery.

I do have a concern though. I just noticed that iPAQ wants 5.0V @ 2A. My DC power will feed 4.8V @ 1A max. Is there any danger in trying this?
 

merlocka

Platinum Member
Nov 24, 1999
2,832
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I do have a concern though. I just noticed that iPAQ wants 5.0V @ 2A. My DC power will feed 4.8V @ 1A max. Is there any danger in trying this?

If the DC supply get's hot and melts that means it coudn't supply enough current.


jk


Since the iPaq is probably running at 3.3v logic, the 5v will get regulated down anyway so 4.8 should be fine. As far as ampers, are you talking about an external battery or a AC/DC converter?

 

joohang

Lifer
Oct 22, 2000
12,340
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Originally posted by: merlocka
I do have a concern though. I just noticed that iPAQ wants 5.0V @ 2A. My DC power will feed 4.8V @ 1A max. Is there any danger in trying this?

If the DC supply get's hot and melts that means it coudn't supply enough current.


jk


Since the iPaq is probably running at 3.3v logic, the 5v will get regulated down anyway so 4.8 should be fine. As far as ampers, are you talking about an external battery or a AC/DC converter?

In the back of the iPAQ, it says that I should use 5V DC 2A input.

My battery recharger and DC power extender takes 4x 1.2V NiMH batteries and it claims that it will supply a maximum of 1A. There shouldn't be a concern with underpowering, right? In the worst case, it won't recharge, from my understanding. Just wanted to confirm this.

BTW, I'm using this device and it has 3V, 4.5V, 6V, etc. I'm going to run it at "4.5V" setting but I wonder if these "voltage settings" actually regulate the voltage for me or simply takes power from different number of voltages. Since the device only takes NiMH (which are 1.2V), I'm guessing that it takes power from all 4 cells and uses some sort of voltage converter/regulator. Hmm.. maybe I should go and buy a voltmeter tomorrow just in case. :)
 

MWink

Diamond Member
Oct 9, 1999
3,642
1
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I understand that NiMH is 1.2V but wouldn't I get 4.8V if I add 4 AA NiMH batteries together (in serial?)? And Walmart sells 4x 1600 mAh batteries for 11 bucks. Would that give me a potential of 6400 mAh?

That is incorrect. If you wire them in series you get 4.8V at 1600mAH. If you wire them in PARALLEL you get 1.2V at 6400mAH.
 

FishTankX

Platinum Member
Oct 6, 2001
2,738
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Translation for Joohang:When you wire them in paralell, you crank up the voltage, but at the voltage it takes more energy to deliver the same amperage, so you have a max of 1600MAH. Thus, your super duper DC power source actually only has 1.5X the energy of your Li Polymer battery.
 

joohang

Lifer
Oct 22, 2000
12,340
1
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Originally posted by: MWink
I understand that NiMH is 1.2V but wouldn't I get 4.8V if I add 4 AA NiMH batteries together (in serial?)? And Walmart sells 4x 1600 mAh batteries for 11 bucks. Would that give me a potential of 6400 mAh?

That is incorrect. If you wire them in serial you get 4.8V at 1600mAH. If you wire them in PARALLEL you get 1.2V at 6400mAH.

Right. That makes sense.

<-- forgot his physics. :)
 

joohang

Lifer
Oct 22, 2000
12,340
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Update: So I got the device but it only supplies 4.5V @ 1A max. The iPAQ requires 5V @ 2A.

But the rating on the iPAQ appears to be one required to operate the device. My battery extender failed to power the iPAQ when it's turned on, but when the device was off, it recharged the internal battery. It just finished recharging all the way and my iPAQ reads 100% full for battery life.

Looks like I'll have to buy that Semsons for 10 bucks after all.