Posted for "Larry Henney" <LHenney@dellepro.com>:

 David,
  
I was equally impressed with some of the new battery technologies.  I
use a 3 amp 12 volt Powersonics battery to backup my emergency bus.
This will run my electronic ignition in excess of an hour (this is after
alternator and main battery depletion (haven't seen it yet)).  The
incredible thing is that my header tank fuel would actually be the
limiting factor in the above scenario.    I throw mine out every couple years as an insurance policy.  The battery
I use comes from Allied Signal for about $20.  Using a battery of this
sort might save you some effort and keep that drill available.
Larry Henney
N360LH LNC2 IO-360 B1
16XS  Ft Worth, TX