If you want to do this, leave at least 32Mb at the end of the disk free. The BIOS screen is in English, even on the Japanese models. It obviously depends on the type of work you are doing - if your work doesn't involve frequent disk activity, then the disk will switch off, and cut the power use significantly. Within Windows 95, you can set various power saving options, such as display brightness, time until hard disk stops, processor speed, PC Card power etc. Use of PC Cards also affects battery life.
Some cards consume a lot of power - modems especially.
Apparently some cards even draw power when not in use, so its a good idea to remove them to maximise battery time. Apparently the software on the Libretto 70, the accuracy of the software is improved, although I have not been able to confirm this. When the Libretto senses that the battery is about to give out, the machine begins a steady bleeping sound, and the charging LED flashes. If this happens, you should immediately save your work and shut down, or attach the machine to the AC power supply. Thanks to Ivan Stern for some of this information.