All newer cars especially bmw have a volt meter on the + or - post clamp, when this meter reads under 14.4 like you said after running it triggers the battery light on your dash. The light is a charging circuit issue almost always ends up being alternator replaced unless broken/ chafed wires
And to touch on the issue you asked between the battery’s you have to use the one that fits your car battery’s location. The length and width of the battery’s are different. The length width and height are your group size . To make this easy plug your vin into a auto website you trust and it will tell you what the oem requirements