Hi JJ,
First off, you stated you have the B-124E battery pack. You only have/use the B-124E battery pack when you expand the capacity of the B-124X primary battery pack. I would venture to guess that you have the B-124X and not the B-124E unless you have a two battery pack system.
The cigarette lighter power connector that plugs into the B-124X (as provided from BlackVue) delivers constant battery power and ground. There is no switched/accessory power being provided to the cigarette lighter (female) connector. This would result in the DR900X Plus being on all of the time (as long as the B-124X battery has a charge sufficient to provide power) when using the cigarette lighter power port cable for the DR900X Plus dash camera.
I have a video explaining the hardwiring cable configuration for many of the dash camera battery packs manufactured by EGEN. The B-124X is one of those battery packs and they all share the same power output terminal pin layout. The first picture is of the B-124X with the cigarette lighter power port adapter plugged into the B-124X. It's a two wire connection. The second picture is a BlackboxMyCar PowerCell 8 (again manufactured by EGEN) and I show which terminal pin layout.
If you were using the DR900S cigarette lighter power connector, then yes you do need to replace it with the one supplied with the DR900X Plus since the number of connectors and its size has changed between the two models of dash cameras.
I'm guessing you want some sort of parking mode enabled in the DR900X Plus dash camera, otherwise why would you have the B-124X battery pack.
The DR900X Plus has two ways to enter parking mode. If the vehicle is stationary for 5-minutes, the dash camera will enter parking mode and it will exit when the vehicle begins moving. The second method requires the use of the 3-wire hardwiring cable for the DR900X Plus dash camera. When wired with the 3-wire hardwiring cable, the dash camera will enter parking mode when the accessory power feed is shut off (ignition switch off) and it will exit parking mode when the accessory power feed is restored (ignition switch on). The motion based parking mode logic is still active as well even when using the 3-wire hardwiring cable (no way to disable that logic if using any of the available parking modes).
There are several additional settings in the DR900X Plus that govern "Battery Protection" (low voltage cutoff and parking mode timer).
It would helpful to explain what your desired behavior (parking mode related) for the DR900X Plus is so it would be easier to let you know how to achieve that behavior.
BTW, I grew up living in MN just north of St. Paul (way back in the late 60s and early 70s).