Hmm, running a laptop during an installation on the battery is pretty hazardous. The bootmgr missing can have many causes. I assume you tried to reinstall again from the recovery partition and got the same message.
One help you could give us to understand the situation is to download and burn the bootable CD of this program
(it is the last entry on the page). Boot the CD from the optical reader and take a picture of what you see (should look somewhat like the picture below). Then post that picture here (use the paper clip).