Even if the window itself is not shown.
As seen with powertop or strace:

‰ strace -f -p 19369
strace: Process 19369 attached with 25 threads
[pid 19499] restart_syscall(<... resuming interrupted read ...> <unfinished ...>
[pid 19467] restart_syscall(<... resuming interrupted read ...> <unfinished ...>
[pid 19456] futex(0x7f7e5effcc08, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
[pid 19444] restart_syscall(<... resuming interrupted read ...> <unfinished ...>
[pid 19410] futex(0x7f7e81ffab08, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
[pid 19408] restart_syscall(<... resuming interrupted read ...> <unfinished ...>
[pid 19395] futex(0x7f7e82ffcc08, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
[pid 19392] epoll_wait(37,  <unfinished ...>
[pid 19391] restart_syscall(<... resuming interrupted read ...> <unfinished ...>
[pid 19390] futex(0x7f7ea1ffab08, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
[pid 19389] futex(0x55846c84a798, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
[pid 19388] restart_syscall(<... resuming interrupted read ...> <unfinished ...>
[pid 19387] select(33, [32], NULL, NULL, NULL <unfinished ...>
[pid 19384] epoll_wait(27,  <unfinished ...>
[pid 19382] epoll_wait(22,  <unfinished ...>
[pid 19381] wait4(19378,  <unfinished ...>
[pid 19376] restart_syscall(<... resuming interrupted read ...> <unfinished ...>
[pid 19375] restart_syscall(<... resuming interrupted read ...> <unfinished ...>
[pid 19374] futex(0x7f7ed4005638, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
[pid 19373] futex(0x7f7ed4005638, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
[pid 19371] futex(0x7f7ed4005638, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
[pid 19369] restart_syscall(<... resuming interrupted read ...> <unfinished ...>
[pid 19394] epoll_wait(49,  <unfinished ...>
[pid 19372] futex(0x7f7ed4005638, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
[pid 19370] restart_syscall(<... resuming interrupted read ...> <unfinished ...>
[pid 19369] <... restart_syscall resumed>) = 0
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] write(5, "\1\0\0\0\0\0\0\0", 8) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 0) = 1 ([{fd=5, revents=POLLIN}])
[pid 19369] read(5, "\1\0\0\0\0\0\0\0", 16) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] write(5, "\1\0\0\0\0\0\0\0", 8) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 0) = 1 ([{fd=5, revents=POLLIN}])
[pid 19369] read(5, "\1\0\0\0\0\0\0\0", 16) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] write(5, "\1\0\0\0\0\0\0\0", 8) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 0) = 1 ([{fd=5, revents=POLLIN}])
[pid 19369] read(5, "\1\0\0\0\0\0\0\0", 16) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] write(5, "\1\0\0\0\0\0\0\0", 8) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 0) = 1 ([{fd=5, revents=POLLIN}])
[pid 19369] read(5, "\1\0\0\0\0\0\0\0", 16) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] write(5, "\1\0\0\0\0\0\0\0", 8) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 0) = 1 ([{fd=5, revents=POLLIN}])
[pid 19369] read(5, "\1\0\0\0\0\0\0\0", 16) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49 <unfinished ...>
[pid 19370] <... restart_syscall resumed>) = 1
[pid 19370] recvmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="U\2\253\7\203\357\3\10\3\4\4\0\0\0\0\0\0\0\0\4\4\4\4\4\0\0\3\37%\2\0\0", iov_len=4096}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 32
[pid 19370] write(5, "\1\0\0\0\0\0\0\0", 8) = 8
[pid 19369] <... poll resumed>)         = 1 ([{fd=5, revents=POLLIN}])
[pid 19370] poll([{fd=3, events=POLLIN}], 1, -1 <unfinished ...>
[pid 19369] read(5, "\1\0\0\0\0\0\0\0", 16) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 48) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50) = 0 (Timeout)
[pid 19369] write(5, "\1\0\0\0\0\0\0\0", 8) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 0) = 1 ([{fd=5, revents=POLLIN}])
[pid 19369] read(5, "\1\0\0\0\0\0\0\0", 16) = 8
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 49) = 0 (Timeout)
[pid 19369] poll([{fd=5, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8, events=POLLIN}], 3, 50^Cstrace: Process 19369 detached


EXPECTED RESULT
marble shouldn't spend my battery when it has nothing to do.


SOFTWARE/OS VERSIONS
marble 26493d125a3f8860fd5c12b96e0ab949c09f7b52
qt-5.14.0 on xorg-server-1.20.6 on linux-5.4