suspend has to keep supplying power to the RAM

When I close my laptop’s lid, I have it set up to suspend for five minutes, then hibernate.

That lets me close the lid and move the laptop to somewhere nearby without using much battery power, but if it gets left closed for long, the thing will hibernate, so it won’t drain the battery.

That’s HandleLidSwitch=suspend-then-hibernate in /etc/systemd/logind.conf, and HibernateDelaySec=300 in /etc/systemd/sleep.conf.

Any other system just gets shut down.

EDIT: Note that I don’t believe that this is necessary to avoid data loss. I think that the default on Debian is to suspend, but there’s another default to hibernate when the battery becomes extremely low, so either way, a laptop sitting on a shelf for a week — or however long it takes to drain whatever battery is left while suspended — should wind up hibernated. But with the defaults, it’s going to have a laptop with critical battery next time you open it up, and with my settings, it’ll have about as much charge as when you closed the thing.