How much voltage does the alternator....
 

have to put out to charge the battery in our 2011 Lexus RX350? Perhaps I am not driving it enough. Temp this morning is -10C or about 20F. Voltage measured at battery with engine running is 13 volts. Thanks in advance. Car would not start this morning. Engine would not turn over...

13.8 or .9 to 14.6 is normal 13.0 is low

battery should read 12.6 if full charged
but if original 2011 it could be time for a new battery now

try the cheap fixes first clean the posts and connections esp the grounds

The voltage should be close to 14v but you also need to know the amps the alt is putting out.Most parts stores can check that now.

Thanks all. The owner's manual says if recharging the battery in the vehicle be sure to disconnect the ground cable. Why is this? The tops of the battery do not appear to come off so can the battery vent properly while being recharged?

If I disconnect the cables to clean the posts then does anything need to be reset? Radio codes etc?

In answer to your questions: You should disconnect the ground cable to protect the cars computer. Yes, they look sealed but they can vent while charging takes place. If your radio has a code it will more than likely have to be re-entered once you reconnect the battery.

I agree, if this is the original battery it is more than likely time for a new one.

Disconnecting the battery isolates the cars computer from a spike in case the battery charger is hooked up wrong.

5 years is pretty much max for a battery.

100 Amp 6/12V Battery Load Tester

You can connect a 9v battery through the cig lighter to keep the memories alive (be careful of polarity though). Your battery even though showing 12.6 volts could have diminished reserve power after 5 yrs and need replacement .Most parts stores will load test a battery free.