I have full power low battery light is on and truck wont start

I have a 2017 silverado 1500. I  Have had it for 2 months.
Sinceday number 2 my battery light keeps coming on and
saying I have low battery. I've charged this battery several
times to full charge. I soon as I hook it backup again at still
says low battery. So at finally died on me. By died I mean
simply would not start. So I pulled the battery out when
bought a new one put it in and it started right up no
problem.  Within an hour my truck was reading low battery
again. I have put battery testers on my battery. I have but a
load on my battery with battery testers. At it as far
exceeded above 12 V. I went to look at a job and when I
got back in my truck to leave I didn't wanna start. I turn the
key a couple times. Eventually at turned over and started. I
got the truck com turn it off turn it back on no problem.
Turn it off turn it back on no problem. Let it set for a while.
May my son want to go for a bike ride. We stopped the gas
station to get drinks for the ride. Come back out. Truck
won't start. Just clicks. I'm assuming that's the starter. My
Low battery light is still on. I have tested it again. I am at
like 14 V. Even where the load it's not going on or 12 V. I
can test my charging system with this battery tester. And
it says it is working properly. So why is my battery light on.
And why won't my truck start?