I'm aware there are many threads regarding battery life issues already, but it doesn't seem like problem has been isolated and described properly by someone (ie. in wiki) yet - however, I'd genuinely love to be wrong here.

I have N810 flashed with latest OS2008 for over a month now, and its battery is really driving me nuts. I'm checking battery charge level with battery-status package. Sometimes it's quite all right, and battery discharges itself slowly when on standby, with wifi/BT on. Sometimes, while on standby AND in offline mode, it drops overnight from 80% down to 5% without any obvious reason. Sometimes when battery charge level is - for example - 50%, and I reboot my Tablet, it jumps to 90% after reboot. Sometimes it drops to 20% after reboot. Totally unpredictable.

I've tried isolate the problem - first off by disabling metalayer-crawler, as advised by someone on the forum. Then I've spotted that Modest sometimes leaves running processes in the background (ps aux | grep modest), despite closing it. But battery still discharges quickly without any regular pattern, even when no applications appear to run in the background.

The very latest example was today at work: I've disconnected N810 from charger at home around 7:30am. At 10am in the office battery was 94%, but I've been using tablet on my way to work, so that's ok. When I was leaving office at 6pm it was... 47%. During that 8 hours device was mostly idle, I've just checked software updates in Application Manager once and that's it! I've even made sure that Modest didn't leave any processes in memory, and closed off all apps as I arrived to the office. When I did reboot battery level dropped to 10%. Insane!

Did anyone worked that issue out?

When closed Modest will spawn a background daemon for checking email based on your stated prefs. So you can check one moment, not do anything, and the next it will be running. You should change your preference to no automatic checking to stop it respawning in the background.

The biggest issues I've had with variability in batter life have always been traced back to the type of WiFi access point that I'm using. Those with WMM Powersaving mode work 100% better than those without. Even a small amount of surfing without WMM and the battery takes a wallop.

I have automatic email checking feature disabled, in both built-in E-Mail app (which is previous version of Modest, I believe?) and Modest itself...

Great, but I have those issues even while in offline mode => no wifi, no BT, but battery still goes down... :(

Some of what I'm seeing matches some of what you see; while my battery life is consistently good, the battery applet is often confused immediately after a reboot, whether crash-induced or intentional.

I think I may have figured this one out. Or at least, I've solved it on my house network.

First, my situation: on my N800 with OS2007 a fully charged battery could remain connected (unlimited time) on my house wifi and the battery applet would report 10 day idle time and 7 hours use time.

I upgraded to OS2008 and on a fully charged battery the battery applet reports only 2 hours of use time.

My solution: change a setting on my wifi access point! I have a Netgear RangeMax WPN824 (firmware V2.0.10_1.2.17NA). On the "Wireless Settings" page of the admin interface I changed the wireless mode from the default (Auto 108Mbps) to (G and B) mode.

Blammo! instant battery life With unlimited idle time on wlan connections I'm back to 10/7 battery reports.

Excellent!
Of course, I stay away from those wierd proprietary extensions, anyway. But it's good to know, anyway.

I always go into offline mode when I finish using the unit and screen lock it. Bluetooth will use the battery and it also prevents wifi from coming on. Also Media Player metacrawler will affect battery life so disabling it helps. Mplayer and Canola are better media players anyway. Mplayer plays a wider variety of video media including .flv (youtube downloads).

I wouldn't suggest to take battery applet reports as ultimate battery charge level indicator. It reflects current CPU usage, hence if for example you would disconnect Tablet from charger with 100% battery level, and then execute Canola (for example), CPU would get very busy. At this particular moment battery applet will show less than 7 hours. But once Canola is executed and idle, CPU would get back to idle state and battery applet again will show 7 hours. I strongly recommend using battery-status package from nitapps.com, which gives current exact battery charge level.


My latest overnight test proved that rebooting Tablet often is probably the only remedy for the problem I've described. Yesterday in the evening I've been browsing web with N810, and just before going sleep I've rebooted it and then switched offline mode on. Battery went down just 3% overnight...