This is great, good work Pali for building OSS BME replacement and for USB mode.

Since you are intimate with the system I wonder if the following are possible in software.

One improvement in the charging system itself would be to have a timed reset or renegotiate of the charging every few minutes for the users who use bicycle dynamos, solar chargers, maybe even home mains chargers when they experience a brownout.
When there is an interruption in charging the N900 will dial back the amps(charging rate) to keep voltage from dropping and even when power is restored like the sun comes out of the clouds or a cyclist hits a downhill the low charge rate is maintained. Cases like this where there might only be one or two sun breaks in an afternoon or ten minutes of downhill for every hour of mountain climb in a long bike tour mean that the N900 user has to remember to unplug and replug when incoming power will be high, otherwise they miss out on that vital charging opportunity. If not standard perhaps having an "unreliable power" option in USB mode which resets charging every few minutes if below a determined charge rate.

Another improvement is if possible to free the charging from requiring the shorted data leads, this might not be ideal for a smart charging system, if so requiring a change in config file would be reasonable. Users who for example have ripped out their USB port or installed an inductive charging system need to also install a battery charge manager board and solder directly to battery connectors rather that using the very nice charge management system internal to the N900,fitting the Li-po manager is tricky with a regular cover and even with a double battery/mugen cover. It would be great to run one wire to a ground and the other to the positive USB pad and actually see my charging, one hack used was to actually solder a switch across the secondary data pads int he battery area, this is a crude hack since it requires removing the battery to switch to normal USB operation.