Smaller Battery

[aliking]

Getting the obvious objections out of the way first:

Pandora's big battery is awesome and the kind of battery life that we are seeing for continual usage is great. There are tons of reasons why someone might not want to consider having a smaller battery and reducing that. This is a given.

However, a smaller battery option would free up some useful, easily accessible space in the main part of the case for hacking in other components. So I was curious; how easy/safe would it be to either swap in a different LI-PO of similar specs[sup]1[/sup] or carefully adapt the Pandora battery[sup]2[/sup]?

[sup]1[/sup] What specs specifically would have to be the same? Would an RC LI-PO battery pack 3.7V, 3000mAh just work? My understanding is that the charging circuits are based on voltage, so could they safely charge any LI-PO to 4.2V without worrying?

[sup]2[/sup]I'm assuming that the Pandora battery pack is not much more than a number of LI-PO cells in parallel in a wrapper. Could you unwrap it and remove a few cells?

If either of these worked, how would the battery gauge cope with it? Would it need tweaking or should it just assume the correct percentage discharge based on the battery voltage?

a

 

[mcobit]

I think the battery has its own charging circuit. So it might not be easily swappable with another model. And I would say the battery has around 5V. As USB runs at this Voltage.

 

[WizardStan]

lipo are not cells, it is one complete mush of battery stuff wrapped in a thin piece of plastic. DO NOT UNWRAP IT!
It is indeed 4.2 volts, this is standard lipo voltage. In theory you could get a similar, smaller battery and the Pandora charge circuits should be able to handle it. The only catches I can think of would be the temperature gauge (the Pandora battery knows how hot it is getting so it can shut down in an emergency, and I don't know how it would handle it if there was no thermometer) and the "time remaining" will no longer be accurate.
Now you just need to figure out where to get such a battery

 

[urjaman]

Also, make sure that the pandora wont hit the battery with too much charge current. It is set at 1A, so
"Generally, cell phone batteries can be charged at 1C and laptop-types at 0.8C, where C is the current that would discharge the battery in one hour." - Wikipedia.
Thus, I wouldnt charge a battery with less than 1000 mAh of capacity without changing the charge current to something less. (This still has the safety margin of the pandoras own current usage (that is taken from the charge current).)

 

[jonjandran]

www.batteryspace.com

I work with Li-po's all the time. Be very careful they can explode.

And yes they do put out up to 4.2v , but you will be using a standard 3.7v Li-Po cell. One thing I am not sure of is the PCB (protection circuit) It sort of looks like the Pcb is built into the Pandora battery ? On the end where the connections are. That looks about the right size. Who would we need to contact to find that out. Because if it is built in then we would need to add our own. Not expensive ($1.70) but AN ABSOLUTE NECESSITY !

You would of course need to be somewhat competent because there would be a need to solder in the new battery. You won't find one with the same connections.

Here's some I would recommend :

The Pandora battery is 3.7v 4000mAH. Size is 44.5mm X 135mm X 6.5mm or thereabouts.

This one is about half power. 3.7v , 2100mAh . It is same width and height and 2/3 as long. 44mm X 90mm X 6mm. Costs is $19.99
http://www.batteryspace.com/highpowerpolymerli-ioncell37v2100mah604490-20c777wh40adrainrate.aspx

This one is about 1/3 the power and about half the size: 3.7v , 1500mAh. 7.0mm x 35.5mm x 65mm Costs is $7.95
http://www.batteryspace.com/polymerli-ioncell37v1500mah703562-2c555wh3arate-ullisted.aspx

The Pcb you would need for it if the Pcb is not hardwired into the Pandora:
http://www.batteryspace.com/PCB-for-3.7V-of-Li-Ion-Battery-2.0A-limit.aspx

Here's the battery that OP is most likely using :
http://www.batteryspace.com/highpowerpolymerli-ioncell37v4000mah6745135-10c148wh40arate-ulunlisted.aspx

As you can see you are not going to gain a lot of room and you will be losing half your battery life. And it will be a decent amount of work.

Not worth it IMO.

 

[aliking]

Very interesting, thanks. I guess I agree it wouldn't necessarily be worth it at this point, but this is good stuff to know.

 

[Tor]

I think the battery has its own charging circuit. So it might not be easily swappable with another model. And I would say the battery has around 5V. As USB runs at this Voltage.

No, and this is important: The batteries don't have their own charging circuits. What they have is a protection circuit, and it's there for an entirely different purpose. Don't mistake them for charging circuits, they aren't.

It should be fairly safe to replace with a slightly smaller battery. The circuit in the Pandora and the software may make some assumptions about the battery's capacity, but in any case it will never try to charge it above whatever is set as a safe limit (probably around 4.20 volts max, as these are 3.7V rated batteries), so no risk of overcharging. The battery charge level indicator may become a bit unreliable, but that doesn't matter much - they're awfully unreliable anyway on any OMAP SoC due to the extremely wildly fluctuating power drain as individual parts of the SoC powers on and off, clock frequencies go up and down, and voltage the same.

And whatever you do - never ever try to disassemble any lithium poly/ion/metal battery of any kind.

 

[TitanUranus]

And whatever you do - never ever try to disassemble any lithium poly/ion/metal battery of any kind.

Ooh - but you make it sound like so much fun! Can anyone confirm if Abu Hamza once tried taking his mobile phone li-po battery apart?