Re: brainstorm: extending n900 battery life (mods)
 

You also need a chip to balance the two spare batteries if you connect them in series, and it's probably a bad idea to not use a protection circuit for preventing overdischarge/overcharge. If the N900 has "special charger" mode like N810, it will eat power down to 4.2V input, at which point your two series batteries will ideally be 2.1V each, which is too low for Li-Ion. Recharging them again after draining them that low could be dangerous or at the very least cause excessive wear&tear on the batteries. In worst case, if one of your spare batteries is older or has seen different use and thus aged differently, the two batteries will have different charge states, pushing one of them way below 2 or even 1V (when one of them gets empty before the other), which basically is "too dangerous to use again"-territory...

Protection Circuits can be found at batteryspace, for example: http://www.batteryspace.com/pcmwithe...02s20-265.aspx

Instead of having the batteries in series and dropping voltage with a linear regulator to 5V, I would have the batteries connected in parallell, and use a boost converter to bring up the voltage to 5V. This thing looks useable: http://www.dimensionengineering.com/lvboost.htm

This would do away with the balancing requirement, for connecting them in parallell you just need to make sure they're both at same level of charge before you connect them together. This would enable you to use a simpler and cheaper protection circuit, such as: http://www.batteryspace.com/pcbfor37...a-1alimit.aspx

Now you just need a charge regulator to make it perfect! The circuit above will cut off charge at 4.35V (or 4.275V if you believe the scan). Maybe a bit too high when considering wear&tear on the battery, but probably safe enough to avoid explosions and/or battery swelling :)

But a device like the one you've just designed already exists anyway, here's an example http://www.amazon.com/dp/B00152OCAQ/, both cheaper and more expensive models available..

Re: brainstorm: extending n900 battery life (mods)
 

Thats exactly what you do ( although not from a eee on standby obviously :) )

From the Specifications

I have charged my N800 twice without flattening it.

Rick

Re: brainstorm: extending n900 battery life (mods)
 

Thanks! I feel like I'm learning a foreign language by going straight to a new country and having to communicate there! I'm not completely dumb (well, not quite completely) but much of what is said here is going clean over my furry head. I can usually work out when something is said that might be useful to me, but often need to check I heard right!

Re: brainstorm: extending n900 battery life (mods)
 

Heat is the biggest enemy of a battery. Unlike notebooks, the N900 doesn't get hot, so this shouldn't matter.

I'd suggest to just use the device without worrying about the battery too much. There's already fancy electronics and software installed to keep care of the battery for you.

Just use the device and be happy. I usually charge my N900 every night and then can use it the whole day without worrying.

Re: brainstorm: extending n900 battery life (mods)
 

Can you give us an idea of your daily usage. Eg.
9am to 1am. How many bars left
- set to 3G
- surf web for X mins
- watch video for X mins, listen to X music
- how often does it connect to internet?
- minutes of voice calls
- ever connected to wifi

Re: brainstorm: extending n900 battery life (mods)
 

X2

AFAIK, A standard linear regulator usually needs a forward voltage 2-3V higher than its output to function correctly. Therefore as the batteries discharge, there is the potential a linear regulator might not be able to correctly control voltage.

Re: brainstorm: extending n900 battery life (mods)
 

I'd say, about 2h of playing music in the car using FM transmitter (you'd suppose this to drain the battery a lot, but it doesn't),
about in total 15 minutes web surfing on 3G spread over the day, about 15 to 30 minutes voice calls,
sometimes taking photos.
The device is always online. WiFi at home, 2G or 3G elsewhere. I set it to connect automatically.

The battery is then usually still half full in the evening. My G1 was half full in the evening too, but only if I did not do much more than carry it around with me during the day, reading a little email.

The N900 battery only begins to drain more quickly when disabling WiFi power management for connecting to the device via ssh.
I currently don't watch lots of video on it.

Re: brainstorm: extending n900 battery life (mods)
 

Thanks very much for the clarification. It does seem liveable for most light days

Re: brainstorm: extending n900 battery life (mods)
 

Yes, definitely. And not light days, well even the N810 didn't survive those with a single charge. :)

Re: brainstorm: extending n900 battery life (mods)
 

I have to add that I don't have the latest firmware currently. So in the end the battery life could be even better in the sales product.