RE: receiver battery
There are various meters with which one can check flight pack voltages between flights and avoid that sudden "sinking feeling." I have an Ace Mini ESV (expanded scale voltmeter) that's about 1 1/2" square X 3/4" and wired with a
Futaba plug. From time to time it's had several other plugs on the end. I don't remember when I got it, but it has surely been over 20 years ago, and it has never let me down.
I make a point to go to the field with a charged flight pack aboard and often take a spare too. I check my packs with my Mini ESV after a few flights, just to be safe. I don't know if these little dudes are available today, but whatever you may get and at what price, it's well worth it, so get one and use it...it will certainly save your plane.