Bullsh.it remark but it is very easy to see if a tank is empty, not so obvious to see how weak a battery is.
Actually on the Twin Star, due to its design, it's
not that easy to see if the tank is empty without looking at the fuel gauges! And somewhere around the same place on the MFD are voltage and current gauges, which would of course be showing abnormal indications if anything was wrong. The G1000 even highlights anything in red/yellow for you! If you do your checks properly, it's perfectly easy to see how weak the battery is.