This might be easy.
Notice how things change when you rev your engine? Your engine moves a bit when you rev it and that movement pull on hoses and wires including the battery cable connectors. You said you just had your battery changed.
A couple of years ago I watched several helpful guys try to help two women start their vehicle. They jumped the battery which started the engine but it died when they disconnected their cables. They ran extension cords to a battery charger and charged the battery for a while. Nothing. I went over and asked when the ladies began having starting trouble. Ever since they’d had their battery changed (on the road) just after they’d left on their trip. Hmm. I gave the battery connectors a healthy twist with my fingers and they both rotated! The ladies had some wrenches in the trunk which was all we needed to tighten up the cable connectors.
You may have the same problem. Almost all battery connectors are dirty, and show white and green chemical growth. When a battery is changed, somebody needs to spend some time cleaning all that stuff off and make sure the little nut that is designed to not be able to get a wrench on, is nice and tight. Try to twist it when you are done.