IO540
The RV10 owner had not fitted a back-up alternator as the glass screen kit have built in batt back-up of at least 30mins.
He also had a stand alone standby battery for Screens/GPS ,No.1 vhf/nav,and transponder with min one hour use as a get on the ground capability.
The N reg Allison engined P210 conversion I fly in UK, mainly IFR, has only one starter/generator.
The drive sheered last week en route at FL180!
There is no provision for a back up alternator, but it also has a large main batt and dedicated stby avionics batt. Combined, good for at least for 1 and 1/2 hours after gen failure, ample to get on the ground in IFR conditions.