[maemo-users] Experience with N800 portable autonomous battery charger

From: Laurent GUERBY laurent at guerby.net
Date: Sun Jul 22 16:28:59 EEST 2007
I've been wondering for a while how to extend the (already quite
correct :) battery life on the N800 for long trips without
power plug access and planned continuous use. 

One obvious solution is to buy another BP-5L battery for 40-50 euros
(*), but changing the battery means rebooting the N800 and recharging
the second battery in parallel means another charger (if the model

So I went another route and bought:

- 4x AA NIMH batteries with charger (1), 
- a USB battery extender with room for 4xAA (2) 
- a USB to N800 power plug adapter, part of a quite complete charger and
adapter pack (3)

For a grand total of about 50-60 euros. 

4xAA batteries output 4*1.2V = 4.8V, not far but below the USB standard
5V so likely to be safe. The mayamax USB adapter says input 5V - output
5.6V 500mA and is a bit bulky so it's not just a cable and probably has
some voltage and power control function.

I discharged my N800 up to the alert noise (no bar left), then plugged
the battery extender plus adapter to the N800 and the N800
started charging right away. In about 4 hours it went back to 4 bars
(indication: 4 hours - 6 days with minimum screen brightness so not
completely 100% charged since it's 8 hours - 10 days IIRC) then I needed
to use the N800 so I removed it from the "mobile" charger.

In theory (see computation below), the 4x AA batteries should be able to
charge nearly two times the N800 BP-5L battery, but I've not tested yet
this hypothesis. 

Another thing I'll test is having the N800 at 1 or 2 bars and then
pluging the extender and continuing to use the N800 to see if while
using+charging the N800 power level goes up, stay the same or go down
(say while playing video and testing with different screen brightness
levels). If it goes down it means that at some point I'll need to stop
using the N800 to get extended battery life. 

If it stays or goes up it means that you can get all the continuous
battery life you want just by carrying the appropriate number of sets of
4x AA batteries (these are quite inexpensive).

Exactly what I was looking for :).

Did someone else tried something along these lines?


(*) All prices with 19.6% VAT included.

(1) 4x 2500 mAh class AA NIMH ~ 10-20 euros often with charger
According to tests, this class of AA battery holds around 2.5 Wh,
for reference BP-5L is 3.7V * 1500mAh = 5.5 Wh (probably a bit less)

(2) ReVolt USB Battery Extender (4x AA) ~ 5 euros

(3) Mayamax USB charger pack ~ 27 euros 
Very nice set: USB Car charger + USB Charger (very small) 
+ USB A male with zip cable + 7 different plugs adapters. I tested
N770/N800 plug, Sony-Ericsson K300i plug, mini USB plug for charging
bluetooth GPS globalsat BT-359.

Note: I could not find a brick and mortar store selling
the Nokia CA-100 USB to N800 plug adapter - I tried 5 stores in Paris
(and it seems more expensive than the Mayama pack anyway...).

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