had something very similar happen to my MIL's car. Lights, radio and such would work. Try to start is and nothing, not even clickity click.
Came over, put my meter on the battery, read 12.8ish. had her turn on the head lights and zoom, below 10v. One new battery later we were good to go. Seen this one before in my clunker years, so I always do an impromptu load test like that when I see similar symptoms, bet you will too now.
That is exactly the test I normally do
But I was thrown two curve balls, 1. It had started an hour earlier just fine. 2. the headlights wouldn't turn on and I'll be honest and say I didn't know that they would without the motor running, but ASSumed not.
Then the dash lights were flaking. Fuses all LOOKED good but I've been burnt on that one before. Once in the shop, all the voltages looked good but flakey at times. By that time, looking at the schematic the time delay relay had gotten my attention as most everything goes through it power wise. I was not even thinking battery (can you say "tunnel vision") ? I've always said
"Lessons paid for are best remembered" I guarantee you I'll remember this one LOL
And I'll check that headlight operation today when I finish mowing and report back. I'm glad some are enjoying and hopefully learning from the post
I had my health attitude adjusted 5 years ago> They went in to do a stent or two. OPPS not so easy this time 
Wound up getting a triple bypass that went sideways. I was in an induced coma for 4 weeks, 1 week in an advanced care facility, then 3 weeks of rehab. Another 12+ months for my brain to unscramble due to the 4 weeks of Propofol and Fentanyl. haven't smoked or drank ANY alcohol since 
