Consider this idea:

TWO BATTERIES

If you rarely use CDs / DVDs, just find some other way, like external SCSI drive or network to a different Mac that has one. You can SCSI dock and shoot over a disk image too. Pismo/Lombard optical drives are usually kind of sketchy and tend to go bad. A flex cable in one of mine cracked rendering the drive virtually useless, but I've gotten by fine with these other options.