Re-cell a Jornada 720 Battery

I'd like to use the newer > 1600mAh cells with my Jornada 720 so that I can leave card(s) inserted permanently.

Q. has anyone done this, and will it affect how the charging process determines battery levels in order to stop an over-charge / under-charge.

Are there any negative factors to consider?

Edited by dusty_dex 2013-03-22 2:36 PM

Been done...read...

http://www.hpcfactor.com/forums/forums/thread-view.asp?tid=10533&start=1

http://www.hpcfactor.com/forums/forums/thread-view.asp?tid=14235&posts=7&highlight=jornada battery rebuild&highlightmode=1#M132915

I last did it with the best 18650 cells I had on hand. It'll work fine.
My understanding is that the charging circuitry will change the battery up to a given voltage, then stop. It's independent of the battery capacities.

I'm not sure how the Jornada does it. Some battery use a thermistor, a heat sensing diode, that when it gets warm, cuts off further current flow. Those types are nice because they let the battery suck up whatever juice it wants until it is full. But there is the danger that the sensor of the termistor isn't in contact with the cell, so it won't sense the temperature and cutoff like it should...resulting in battery failure. This is rarely used these days.

Most LION cells use a voltage feedback circuit that cuts off when it sense a slow down in the current flow after the voltage has reached a predetermined level. Those little printed circuit boards you can buy on eBay to protect your 18650s from overcharging use that method.

Fancier laptops actually measure the reverse bias, monitoring it when it reaches a certain level. Most all laptop batteries have this circuity built into the battery itself. It wouldn't do much good to it on the motherboard, since you may be using an extended battery, or even a newer battery with different storage capacity. Still some older machines used circuity on the motherboard to control charging measuring current flow. Ugh.

Most

I just tried recelling a cell pack for my HP J710, used a pair of new Ultrafire 3800mAh (got from HK through eBay @ USD2.99 each), BUT the lengths of these new ones are a bit longer than the originals (SONY Enertec 1950mAh), needs some effort before I can reassemble the battery pack. Also charging doesn't go up to the expected voltage, Current from the Ultrafires is unstable, sometimes up sometimes down. I find that the voltage drops drastically after 30 minutes of continuous use, then levels out at 33 percent and keeps going for another 7 hours ( I use the media player for non-stop music play at 80% volume, as well as typing some articles on the machine) before running out of juice. Not that impressive for those specs, right?

Then I switched the Ultrafires with a pair of Sanyo 1800mAh (salvaged from a dead HP laptop battery pack) and they seem to run well, giving about 9 hours of work and play.

The other 4 from the laptop pack couldnn't take a charge inside the Jornada pack, so I used them in a China-made LED torchlight-cum-battery-pack-for-mobile-phone, and yeah, each pair provided my SK17i (sucking on 1200mAh) with two power backups on one full charge.

I am also trying to getting a pair of new Sanyo 1800mAH from an electrical shop locally (in Kuala Lumpur, Malaysia) @ USD10 each. Well, they may be new to me, BUT not exactly new, because these replacement 18650s don't sell well here, so I suspect the ones I bought may have been manufactured many years ago, I have yet to try and see how those perform.

Having had similar problems with an Apple Newton battery pack, including battery length.

I just wonder if it's worth all the hassle (sourcing the correct batteries) if they won't charge correctly.

Does anybody know if there was a battery holder that took removables instead? Much simpler to refresh tired ones.

Edited by dusty_dex 2013-03-28 5:36 PM

If I am not mistaken, the NEC 400 has a battery holder with springs as contact terminals, you can swap AA alkalines with rechargeables NiMH or NiCd, BUT that is only for the NEC 400 which runs a greyscale screen. Previously I used to own a Sharp Mobilon 4500, when its battery pack konked out, I couldn't recell it with other lithium cells due to the thermistor failure when I pry the pack apart, making it impossible to charge the batteries using the unit and ac adaptor. Lucky for me, the compartment have ample space for a pair of coil terminals, I did managed to slot in removables which I recharge using an external 2 -cell 18650 charger. This situation cannot be applied to the Jornada 7xx due to the tightness of the battery casing.

Me too would also like to get hands on any battery holder to serve my 710.

Had a wild idea once, BUT never tried for fear of unforeseeable danger: I thought of using a makeshift cable with a USB male plug on one end and a plug similar to the ac adaptor plug (for the Jornada)on the other end, maybe I can make use of those external mobile phone powerbanks (those that house 2 or 4 pcs of 18650 cells) to supply extended power to the unit (also charging the unit's battery pack). BUT I am not too sure with the specs of electrical voltages and currents. So it remains a thought.

I know these things may sound silly to some (as if I have nothing better to do), BUT believe me, here in Malaysia we sometimes have to make do with modified items, not everything we see on the net is available here.

Yep. I'm having to use an external booster pack for the lousy Newton battery. It will hold 8 AA rechargables. Without it, the normal battery can't be relied on to give fair warning of power failure.

There is a company in the UK selling new Jornada batteries. But they're an eye-watering £43



Edited by dusty_dex 2013-03-29 2:16 PM

And with regard to "new," how can that be with a J-720, a device of considerable age?

I've been looking for a J-720 battery, too--but unless the sellers have re-celled the batteries themselves, those batteries are ten-years-old...

I'd love for someone at hpcfactor to go into the re-celling business. I'd be the first customer.

Jake

I'll post the link when I get back home. You can ask them yourself.

Good news with my newly bought Sanyo 1800mAh 18650 cells. I snipped two coil springs from an old battery holder and managed to squeeze them in between the cells (did i mention they were a bit shorter compared to original Sony Enertecs) and they fit snugly enough to provide a stable current.
Using Battery Monitor to check the voltage drop curve, the drainage is quite constant except for one part where it suddenly drop from 33% to 0% (and triggered the 'main batteries weak' warning) and then it goes back up to 33% again. That was after using it continuously for 9hrs 40 minutes (with music mp3s running at 80% volume using WinAmp and equaliser) and typing on Pocket Notepad (also running CE-Star Suite for chinese input) for 3 hours non-stop. And I had the display at its brightest most of the time.

the last 33% gave me another 50 minutes of usage before automatically shutting off.

This re-celled pack took about 4 hours to recharge fully.

I have two other original old packs which when fully charged displays only 100% for a brief moment and drop to 80% quickly, then normal onwards. I don't know how reliable 'Battery Monitor' is in monitoring the current, BUT I still get 7 to 8 hours of uptime from these. Not bad, right?



Edited by roychanyl 2013-03-30 3:57 PM

Not bad at all. The 100% charged shouldn't last long...because as soon as it starts draining it automatically falls to the next level for reporting. But in reality, there is a lot of usage between 99.9% and 80%.

Some 18650 cells look longer because they have overload circuity built onto the end of them that you cannot see until you cut them open...although there are minute difference in production sizes..though most are about the same.

I guess some are 18649s and others are 18651s...

Oh silly me, should have known that earlier, anyway thanks for the knocking, Rich.

you may be right there, sometimes I guess they use measurement tools (when on the product drawing board) that are not accurate in the first place, hohoho.

This is the kind of joke I used to have back then when my previous boss keeps on complaining about his name not printed one or two mm higher/lower on his namecards, and guess what he uses a china-made cheap plastic ruler to do his measuring. Some of the ticks or markings are even missing.

Edited by roychanyl 2013-03-31 5:03 AM

Here is the link to PinnacleMicroGB, just enter jornada 728 (or compatible model), into the search box

http://www.pinnaclemicrogb.co.uk/newcart/search.php