DM gave good advice. I'll add one or two things.

Always charge your packs overnight before you go to the field, 12 hours minimum, 15 or a bit more is better.

Never fly more than about 3 flights (max) before checking the remaining capacity in your receiver pack with an Expanded Scale Voltmeter (ESV). Then check it every flight after that. You can buy an ESV through Tower Hobbies for about $15, and it's the best investment you can make in this hobby.
Dennis-