do you know?

Shannon,

 

OK, you have the right attitude!

 

Your battery may only be useful down to about 9 volts.  I know some of my systems fail when they go below 8 volts - Engine monitor shuts down, air-data computer stops working, maybe the radios/GPS pack it in.  The starter motor won't work, just in case you need it.  The resistance devices, like lights,  may continue to work, only dimmer.  So, you must not rely on the amp-hour rating of the battery - maybe someone will do some tests - because it is not useful all the way to empty (0 volts). 

 

Also, if the charging system is failing or the alternator is not large enough, the battery may already be dragged down by the time the problem is recognized.  If the battery is old, it may not have the load life you need.  Nuckolls has proposed using 2 17 amp-hour batteries in parallel and replacing one of them every year to help with the age problem.  I know that a failed B&C sealed battery will not drag down another - I have done that test.

 

One of the reasons I chose the LASAR electronic ignition is that its backup is not tied to the electrical system - it reverts back to magnetos and, each magneto backs up the other.  It is not on the essential bus. 

 

I do know some folks running electronic only ignitions with one or two batteries, but only one electrical system bus, one alternator - no backup.  An all electric airplane is an interesting challenge what with multiple alternators, bus multiples, interesting switching, but only one engine.

 

That's all I know.

 

 

PS It's OK, we're not going to get out of this life alive.