Our battery is draining very quick... We need help

Hello Everyone. We have been preparing our robot for our first tournament of the year, and when we have driven on our field just to practice (without connecting to the field) our batteries have been draining normally. When we plugged our remotes into the field yesterday to have a practice match, our batteries almost immediately drained and we had to drive our robot about two feet in front of the net to make a ball in the high goal (normally we can shoot from the back of the field). The thing that perplexes me is that our LCD said that the voltage was 7.56V (after the match), we had a charged backup battery, 4 brand new charged batteries, and all charged batteries in the remotes. The remotes and cortex showed red lights for the robot which indicates a dead or almost dead battery. We only used the batteries for a full match which is like 2 minutes. In practice we can drive for a full half an hour without having to get as close to the net as we did. It seems as if when we are connected to the field, our battery drains quicker. Has anyone had this problem before, and does anyone have any suggestions. Thanks in advance!(There are pictures of our robot below.)
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I don’t know if it is related, but were your robot batteries recently purchased?

We bought 8 new ones at the beginning of October and they don’t hold a charge overnight, we have to charge them right up to the time we use them.

We informed VEX of this and they are having us send them back for analysis.

We have 8 older batteries that don’t have this issue.

What is the voltage of your batteries when they come off the charger? 7.56V is consistent with the battery being flat, in my experience. When I have measured batteries in good condition coming straight off a vex charger they have usually been just over 8V.

were you using any other motors that you weren’t before?

The voltage of my batteries is around 7.8V when it comes off the charger, give or take a few. Okay, that makes sense, they might be dead. We were not using any other extra motors at the time.