The ones you pictured are Known as superseal connectors and a pita to use to be honest.
Cant remember if you also need a removal tool to get the connectors out.
Years ago, when caravanning off grid, I used to work with two batteries for the caravan - one in the boot of the car on charge, the other in use in the caravan. In the boot, I had a cheap, mains, three pin 5a in-line flex plug socket. on the battery I had a plug, with crock clips. Providing I got the crock clips on the the correct battery terminals, as the 3 pin mains plugs were polarised, to wrong connections were possible.
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