Both, thanks for asking! Let me somehow put things together on why I’m not using external battery charger or using it rarely (and therefore not swapping batteries).
Similarly I’m usually leave my phone connected, even overnight, even when battery at 100% (red LED light off), to two 8000mAh power banks (using just black USB-A port) or to one 18000mAh power bank (using just outer USB-A port, it charges back to its full capacity much quicker). Doing so while, for example, by going out for some walk I can rely on my phone even if I stay out for longer than intended.
Also and sure that I’m disconnecting my Librem 5 regularly down to 50% of inserted battery capacity (either at home or not), but my main reason why mostly leaving phone connected to power bank is to have more peace for myself while not focused anymore not to overlook when it will turn off by itself (empty battery related, which isn’t healthy battery stage for it anyway).
Also, with my current thoughts (trying to be short), I might use car charger to recharge one of my USB-DCP protocol supportive power banks (carefully selected from my side to be used with Librem 5) yet not to charge my Librem 5 directly with any car charger (when some hours spending there), especially if some car charger do not negotiate USB-DCP charging protocol with the Librem 5 at all.
And whatever way I choose to recharge my Librem 5 this is most important, here related, note (that I should not forget to link):