J680E: Disconnecting main battery can run button cell down FAST!

A warning: I removed the main battery from by J680E a few days ago in hoping (*) to prolong its life and minimize the number of charge cycles as I unplug it to move it from room to room. Today I left the J680E disconnected from the mains for about an hour and when I came back it was complaining about my brand-new button cell being nearly run down.

I have a WiFi card in mine, and I think this has something to do with the WiFi card's need to remain powered peridically during standby, or ot doesn't power down completely. I'm not complaining and I don't expect a workaround - just keep this in mind if you remove the main battery for safekeeping.

(*) I have had terrible luck with laptop batteries. I have had two laptops, and both of their batteries failed after less than 6 months in service. Since J680E batteries are bound to be harder and harder to replace in the years ahead, I am thinking it would be best to just leave the battery unattached most of the time. Of course the 680E always stays plugged in. But I carry it from room to room in the house, and each time I plug it in the unit starts another charging cycle. That's exactly how I seem to have kileld my laptop batteries...

Well, I guess the button cell was meant for keep the ram memory intact while we change our batteries. I reckon it meant a 1~2 min interval at most ... but its good finding for the rest of us.

Do you need a CR2032 battery? I can send one to you.

As for the main battery, I think the battery guide recommends recharging when it hits around 50% or something. The good news is that when they die down, you just need two 18650 batts to refurb it. See other threads for details. Just search "18650".
Two piece (2400mAh) come to around $18.

With increasing capacity, we can only expect longer life if we refurb it.

wsanders,

Have a read of the best practices guide:
http://www.hpcfactor.com/support/cesd/h/0015.asp

It coves the basic should and should nots when storing batteries.

The Coin Cell is designed for one thing and one thing only; vRAM integrity conservation.
When the main cell is out of the device, everything else in it except the main RAM and RTC (Real Time Clock) is shut off from the circuit. In this state the device cannot start up at all unless AC is applied, or the battery replaced.

The main purpose of the Coin Cell being there, however, was for when you discharge the main cell too heavily. The Coin Cell provides the current against whatever reserves are left in the depleted main cell to keep the devices RAM powered. In this state with a healthy main cell you can keep a device doing for upto 'weeks'.
As Snappy! said above, when on its own the 3v cell (remember it's a 12v device) is just sucked into the system at a steady rate of knots.

By constantly using it on the mains, that is the fastest way to kill any battery. While Lithium Ion cells do have better charge circuits in them, preventing over chargin, they still shouldn't be perpetually on mains. The best thing you can do with a battery device is use it (and read the guide).

heheh. i also have a question. if i ran down my battery to 6.1V will that damage it? it was 7.1 V just before that. of course i put it on the charger at once. it's a 720 battery
and i've just had it rebuilt it with new 2400 mAh cells
it lasted for more than 8 hours (8:18) with a 95% charge. i was browsing (on the 728 and with RDP too) with wlan all the time!! with about half brightness. hehehe

oh and i measured the voltage with the hp diagnostics.

Edited by cmonex 2005-04-17 12:59 AM

ok no need for an answer. just was worried

I am afraid that as I do not know the voltage specifics on this I can't help you.

oh, no problem. thanks anyway

Nice! I think I am going to refurb my 680e batts soon ...

8hours with wlan surfing!! wow!

It is clear that there is some bug or feature that causes the coin cell battery to attempt to power more than man memory, or my cell would not have run down in one or two hours without the main battery (but with the WiFi card) attached.

For a WiFi card to remain in sync during a 'standby' situation it has to maintain state of some kind. I believe that is what ran down the button cell.

As for the battery best practice page, it is correct in its description of LiIon cells. LiIon cells are good for only 500 or so charge-discharge cycles, but even top-off charges count for a fraction of one of the 500 cycles.

The main problem is that so many charging circuits are badly designed or buggy. My StarTac cell phone treats its batteries exceptionally well, and my LiIon cells are just now starting to lose capacity after about 5 years of daily use.

My Compaq 1750, OTOH, and an old powerbook I used to have trashed their batteries ater only a few months because their charging software and-or hardware was crap. LiIon batteries are extremely sensitive to overcharging, and I think the computers just overcharged them to death.

Fortunately, as everyone pointed out, replacement cells are cheap and plentiful if you're willing to "hack your pack".

more than 8!!!

hehe

but when you did refurbhish your MP 790's batt, didn't that batt last that long?