A total of £175,000 is being spent on mothballing the custody suite at Mold police station in Flintshire, which closed this month.
North Wales Police want to keep it available as the long term future of Wrexham's high-rise police station is uncertain, it has emerged.
Staff from Mold have been redeployed to custody suites at Wrexham and St Asaph, Denbighshire.
But a police authority meeting was told the future of Wrexham is now in review.
Ian Shannon, the deputy chief constable, told a meeting of the North Wales Police Authority that to keep open Mold's suite of cells on a permanent basis would have cost £750,000, and it was necessary to maintain it to an operational standard.
'Money well spent'
He said this was because of the uncertain future of Wrexham police station and its cells.
He said Wrexham was an expensive station to keep open, and its long-term future was being considered under a police estates review.
Mr Shannon said it was vital to keep the suite at Mold to remain resilient and it would be money well spent.
The suite closed on 8 July 2011 and a report to the authority's professional standards committee said the impact would be monitored.
It will still be available as an important reserve for special operations and during seasonal times like New Year's Eve.
Spending of £175,000 would involve essential improvements only, including upgrading of the CCTV, fire alarm and ventilation systems.
Without this work the site could not remain open as a contingency location.
To maintain Mold required five police sergeants and five civilian staff, said the report.