Hi there people

We are in the process of getting the Certificate of Airworthiness for our Glasair powered by Renesis 4 port.

Our AP is questioning the electrical system and wondering if we should have redundant supplies in case of electrical system failure.
Can any of you make comments on risk or preferred systems.

Our setup has one automotive 40amp alternator and two HC20 (PC680 equivalent) paralleled (two batteries are used due to physical location) and mounted in tail for W&B and to keep cool.

My planning was:
1. Keep battery cool
2. Replace every two years
3. Battery Failure modes:
Open circuit cell - Alternator and second battery do the job (No indication that one battery has failed)
Short Circuit cell - Battery voltage drops and overcharges ??
4. Alternator failure modes:
Open Circuit - Low current and Low voltage alarm with 30min electrical reserve capacity
Short Circuit - Charge circuit fuse blows then same as open circuit

I understood that a shorted cell was very low risk in AGM’s if not overheated.
I thought creating redundancy may introduce other failure modes.

Appreciate any feedback.
Steve