Went to the country by train for one day, having to contact people there, and needing GPS.
Brought power monkey battery and solar charger, just in case.

result:
100% CPU bug inducing drain even before using GPS (pre PR1.2 niceties... well).
Because of massive enforcement of micro USB norm, N900 won't charge on data cable (on USB output of either the battery or the solar panel)
=> phone dead before lunch. Yay.

But with PR1.3 and a soldered charging cable, life is much safer nowadays...