I hate having to depend on batteries, and thinking perhaps that in the future the useful life of my N900 will be limited by the life and availability of battery replacements.

One of the awesome qualities of machines like the Zaurus SL-C1000 is that you could use it without a battery when the OS allowed for it. The only limitation in that case was that you couldn't use the CF slot, but useability was not reduced substantially.

I think what causes this issue with the N900 is bme, isn't it? And I just saw Pali mention in the KP 52 thread that a replacement to bme will take place in the near future.

Isn't it possible, from the point of view of the hardware, to run an N900 without a battery, simply with the USB charger connected?

It takes for a depleted battery around 3 hours to be fully charged, and I can't think of a single instance where I have run down a battery in less than 3 hours, so the USB port could theoretically supply enough juice even in peak draw conditions.

Or is there some other hardware limitation? As in, perhaps it is impossible to derive electricity directly from the USB connector to the mainboard without the intervention of the battery. How would it be possible then to swap batteries with the USB charger connected? I've seen it done, but I suppose there could also be a capacitor or something else, although I doubt it.

It would be really good to have this capability to future proof the N900.

I'd imagine, you could upgrade the battery with any 3.7v lipo cell. If you don't mind a big cumbersome, heavy mod, you could theoretically add a 10000mah or more 1s, or 1sxp lipo pack, and devise a way to connect it to the original leads. The stock battery is 1250mah, so well, you do the math .

Add a few caps of the right rating, and you could swap out that pack, to a ac rectified dc power source using a switch without rebooting. Or ideal diode mosfets could allow you to parallel two power sources (ac/dc rectifier (adapter)) and a battery. I use something liket that for a dc atx power supply for an itx amd 5600k fm2 system, that switches fine from a smps and a floating 12v 18ah sla in the event of a power failure. The power supply senses when the battery's voltage gets too low, and gracefully shuts down the system.

Just for the love of god, use a protection pcb on such high capacity diy lipo systems, and fuse it to help you sleep at night.

Really, all you need i would imagine, is to get a 3.7v source to the two +/- pins where the battery goes. Your source of power is endless, solar, mechanical>electrical (hand-crank & big caps lol?), big or small batterys of various voltage with a sepic regulator, and the right protection from overdischarge, an ac/dc adapter with a variable voltage output, or use a sepic to get the right voltage.

Just fuse any custom mods you do, pcb protect lipos/any rechargable battery from shorts/overdischarge, and don't turn your n900 into a charred several hundred dollar paper weight.

Personally, i carry around a 2s 7.4v 1800mah lipo, with a 5v ubec regulator attached to a female usb lead, with the data pins shorted. Get a few charges out of it per pack charge, and the same goes for my nook color and a 14.8v 5000mah pack i have (sucker draws 25 freaking watts, or 5v/5a when the battery is low and its under heavy load). But thats almost a half kilo pack. The ubecs are ~25g, and you can use any 1-6s pack (lipo,life,li-ion). For ~$30 you can build one of these, and draw up to 5a of current from a $10 ubec. Thats like 5 n900's , or a tablet and other 5v devices depending on the current draw of the tablet. Capacitors can help prevent voltage drop under high current spikes.

Oh yeah baby. I remember how surprised I was in the early days of my N900 ownership when I swapped batteries with the charger plugged it and the damn thing just switched off.

Once i read a command on this forum to temporarily suspend those watch-doggy style scripts to just give enough time to swap batteries, but i do not find it now.
Also because of the magnet for the external card, you do not want to try this at all with swap on an external partition!

Yup. The idea was/is to "stop bme" and then make your N900 consume as little power as possible (offline, nothing running, etc.). Supposedly you get a couple of seconds to swap batteries.

Although I cannot prove it anymore in one of my many attempts at unbricking one of my N900s (see around http://talk.maemo.org/showpost.php?p...&postcount=450) I could easily turn on my N900 being plugged but without battery and type stuff at the U-boot console and (attempt to) boot the kernel.

I'm talking MANY seconds, not 1 or 2. Obviously this may (or may not) have had an impact in my failure to unbrick it. Probably the poor thing was in some electrostatic limbo (after leaving it rest a few months I successfully unbricked it..)

@eleseur: You really know your batteries! What I would like however is to not have to use a battery (and also, potentially being able to use it with some sort of AA battery adapter).

Yeah, the bme thing I think is possible. I've seen a video in Youtube of hot battery swapping. I think you have 30 seconds before the system shuts down.

If the bme replacement could actually allow for operation without battery it would be awesome. I really think it should be possible.

something is going on