Smallest/lightest battery?

[Sully]

Come to think of it, does a battery have to be TSO'd?

From another Advisory Circular AC23-27,
Applies to "old or out-of-production general aviation (GA) aircraft, or other GA
aircraft where the parts or materials are either difficult or impossible to obtain."

2. BATTERIES. If one type of series 35 battery (e.g. a Gill 35) is approved as original
equipment or a PMA part, and another type of series 35 battery ( e.g. a Concord 35) is PMA
approved for some aircraft models but not your model aircraft, you may install the alternate type
of series 35 battery and document the installation with only a logbook entry. This applies to all
series 35 batteries. This philosophy also applies to other series, such as series 25 batteries.
However, this part substitution is permissible only as long as the batteries are the same weight,
within plus or minus one pound, and have such similar physical characteristics as to enable the
use of the same securing or attaching devices, mechanisms, or containers.

Approval: This is a minor alteration and you may document it by a logbook entry. The logbook
entry must reference the original and replacement manufacturer's identification or the
performance specifications of the original and replacement battery.

Oh, the joys of an IA

 

[Nuchatlitz]

Why not mount it on the firewall, get rid of everything back there including tray, cables, solenoids. ACA has drawings for that. Extended baggage Explorer must firewall mount. Save weight. Or maybe a Decathlon doesn't have the firewall space with the inverted oil?