BeagleBoard Battery test

Perhaps the most important strategy is not to worry about it :-)

It’s possible to get very deeply into it, but for most users it won’t be a problem. The principal considerations are:

• Don’t charge the battery continuously with a current greater than its rated maximum continuous charging current. This should be obvious, I hope. If you were to exceed it, the electrolyte would dry out and the battery’s capacity would be lost.

• The clock/calendar uses current continuously. The battery also has a “self discharge current” which you would have to calculate, and which is equally continuous. Many computers are only powered up intermittently. You would need to average the number of hours of being switched on over a period of, say, a week, and make sure the charge put in over that period is more than the charge taken out over the same period. Current multiplied by time.

The latter current is the minimum charge current you can get away with, otherwise the battery will gradually run down.

Subject to that, it’s anyone’s guess what strategy yields the best life!

What I read from the datafiles is, don’t discharge it to deep. The battery I use can do 100 full charge cycles or 1000 20% charge cycles, so the more you have your computer on, the longer the battery lives.

But I think the ‘don’t worry’ strategy is OK. Worst case: you leaf your computer off for a month every time and the battery gets very low, you can do that 100 times, so more than 8 years => no problemo.

Thanks Dave and Peter. The reason I asked is that I don’t want to have to replace the battery too often. It’s not the cost of the battery, which is cheap, but the hassle of getting the soldering done – I don’t trust myself to do it. I will just ensure that charging is on every time I use it. Peter’s first sentence confirms what my Son, a Physicist, told me.

I will just ensure that charging is on every time I use it.

The whole point of the Configure Plug-in is that you don’t have to worry about that, just turn charging on and forget about it, it will ensure charging is enabled each time you power up the BB.

...hassle of getting the soldering done…

Perhaps there’s a suitable combination of non-surface-mount cell and battery holder available¹.

¹ I’ve not checked the dimensions of this one.

The BB battery isn’t surface mount, it’s through-hole, just very small!

non-surface-mount non-through-hole

“The whole point of the Configure Plug-in is that you don’t have to worry about that, just turn charging on and forget about it, it will ensure charging is enabled each time you power up the BB.”

This is what I meant.

I have tested the battery on the BeagleBoard some time now and noticed a few things:

Settings 3.1V, 25 uA
The first few days (full bat) during the night the battery discharged and during the day it charged to it full capacity (3.1 V).
Over the holidays the battery got discharged a lot more (2.587V) and during the daytime charging it didn’t get loaded to the full capacity but to 2.72V. The next day it was discharged to 2.587V again. This happened the next few days.
After this I changed the ‘Charging settings’ to 3.1V, 150uA. This way the charging is 6x faster and the battery got fully loaded again.

I loaded the battery for 6 hours, so discharging for 18 hours. Loading with 25uA means it discharged with 25/3 = 7uA/h. This means a 5mAh battery can last 5000/7 = 714h = 29 days.
Not so long.

For those of us whose BeagleBoards have Panasonic vanadium lithium batteries, the document that specifies charging conditions is here

This implies that the voltage should be set at 3.2 V. I’m surprised at how high the permitted currents are. I decided (for no good reason, really) on a high capacity battery (100 mAH), and I find that I could charge it at 4 mA if I wished.

So it does look rather more tolerant than I thought.

Seeing a few comments on the newsgroups recently by people saying that their BB battery isn’t charging back up to 3.1V, or is discharging quite quickly, is anyone else having problems with their battery? Mine gets up to 3.1V happily. Admittedly it’s usually switched on 24/7, so I don’t have a problem with discharging over time. I should leave it switched off for a week and see if it keeps time, I guess.

Mine is usually left on 24/7 as well. If I didn’t do that then it would probably run flat because my typical use case (debugging fun USB things) doesn’t involve running the boot sequence.

At some point I should really sort it out so that the charger settings are stored in NVRAM…

At some point I should really sort it out so that the charger settings are stored in NVRAM…

Once Dave’s got writing CMOS to the card sorted, we can put it in there and change the Configure plug-in accordingly, I guess.

You can put it in the CMOS with or without me. The Configure plug-in, I agree, needs my stuff going.

Sorry, that’s what I meant.

I know it’s been a while since this was last discussed, but what is the current state of play with the battery charging tool/configure plug-in. I’ve just received my battery and will be fitting it over the weekend so it would be nice to get charging sorted at the same time.

To my knowledge it’s still working fine. Which battery are you fitting?

The one I received today from CJE <http://www.cjemicros.co.uk/micros/individual/newprodpages/prodinfo.php?prodcode=VAR-BBBXM>. Going onto a BBxM, but I’ve lost my soldering iron, so I’m off to Maplins in the morning to get a replacement. As my Antec is over 30 years old, it’s probably due for retirement anyway!

The correct settings for that are 3.1V and 25uA.

Thanks Andrew – installed and charging now.

If you read my comment from Jan 13, 2011 11:29am you will see that 25uA is a bit low. You’d better use 150uA.
But it really depends on the time your machine is on/off.

On switch-on for the first time the battery was reading just over 2.6V. After about three hours it has reached 3.084V, which it has stayed at so I assume it is now fully charged now. My BBxM is on 24/7 as it is standing in for my failed (again) Iyonix and running my main apps (Netsurf/Messenger/Netfetch/Sunfish/RDPClient/Organiser/7Backup/
OvPro/Techwrite/DigitalCD/etc).

I think the battery charge/discharge cycle is low voltage when discharged, rising gently up to a plateau where it stays while it is charging and once it approaches fully charged, the voltage gently starts rising again.