In article ,
"Oscar" wrote:

I fly a Cirrus SR22, an all-electric plane. It has dual-redundant power
busses, which makes total electrical failure unlikely, but if it does
happen in IMC it can really ruin your day, so I'm thinking about a
backup plan.

You've got two alternators and two batteries wired together in a way that
can withstand multiple failures and still keep essential electrics going for
an hour. You've already got the backup you need. Any more toys is just
going to be a distraction.

Unfortunately, there are some common mode failures that can cause a
total electrical failure in a Cirrus, notably a failure of the MCU, or
the essential-bus side of the isolation diode shorting to ground. Both
of these could happen if, for example, water got into the MCU. This
(water in the MCU, not TEF) has actually happened in the SR22 that I
fly, at least apparently. After one of the recent winter storms here in
Socal the plane was grounded because of unusually high discharge rates
from both alternators. The problem went away when the plane dried out
and could not be reproduced. This is what motivated me to start
exploring portable backup options. IMC tends to produce a wet airplane.

Sometimes I think you Cirrus guys have more money than brains.

I think that could be said about pilots in general.

rg