WARNING: The following contains spoilers for Detective Comics #1053, on sale now from DC Comics.
After the events of Joker War, Batman lost most of his large fortune and that has left him with some operational constraints. Chief among these is his base of operations. Having to vacate Wayne Manor and move to the city meant that the old Batcave wasn't a viable option anymore. Instead, the Dark Knight had to come up with new micro-caves in Gotham's old tunnels and sewers. Although the Batman usually prepares for everything, there's one serious design flaw in his new Batcave.
The Bat-Family have been operating out of one of the micro-caves whilst they investigate the new Arkham Tower but they were discovered in the conclusion of Detective Comics #1053 (by Mariko Tamaki, Max Raynor, Luis Guerrero and VC's Ariana Maher). The Party Crashers, former Joker henchmen and current Arkham Tower muscle, stumbled on the base and began an all-out assault on the vigilantes. Worst of all, the heroes barely saw it coming.
Batman has had to move his new caves a few times since setting them up, whether it be because of people getting too close or planned maintenance on these very public tunnels. It's still cost-effective as he doesn't have to build most of them from scratch but some still require a lot of effort to set up, back-breaking labor even. However, that inexpensiveness is also their flaw. There's no security. The Dark Knight can not afford anything like that anymore. That combined with the fact that anyone could stumble on the caves at any time exposes the serious flaw in them.
Batman has been lucky up to now but the Bat-Family not so much. The Party Crashers knew about the many hidden pieces of architecture below Gotham, including the entire city that lies underneath it, which they were using for their illicit dealings in this story. They didn't know that the Bat-Family had set up shop in these tunnels too and were simply looking for a leak in their own organization. All it took was a little bit of knowledge about the city's inner workings and the heroes were discovered.
If they had any amount of security, the Bat-Family could have seen it coming and at the very least escaped before they were discovered. They could maybe even have laid a trap for their attackers. Instead, they're pinned down in their own home with more and with more Party Crashers closing in on them. If they do manage to defeat them, they'll have to move. What about the equipment that's already set up in this cave? They can't exactly abandon it, otherwise, Gotham's villains could get a hold of the Dark Knight's advanced tech and computer systems.
This threat of discovery has always been there, whether it be villains, the police or just weirdly nosey members of the general public. The original Batcave had an entire river separating it from the rest of Gotham. That combined with its state-of-the-art security systems meant that there was virtually no hope of villainous invasions unless they had insider knowledge on how the cave worked. These new caves, however, are inherently flawed. It may be best to go back to the drawing board and come up with a totally new Batcave idea, otherwise, Batman and his allies risk meeting their end simply by chance, as is the case here.