Calgary police Staff-Sergeant Brad Moore said 237 batteries were taken from 79 school buses sometime between 2 p.m. on Sunday and 5:30 a.m. Monday.
Kyrie Geurts, assistant general manager at Southland Transportation, said more than 400 students were affected.
She said their suppliers rushed out new batteries and mechanics worked furiously to install them so the buses were up and running by the afternoon.
Staff-Sgt. Brad Moore said multiple individuals were likely involved.
"This is the first we've had of anything large and significant as far as that many thefts of batteries in one location," he said. "We're still looking at all the leads as to why this might have occurred and what the uses of the batteries might have been for."
He said there was a reason the thieves were able to get easy access to the buses, which are kept in a gated yard that does have security patrols but is not monitored around the clock.
"(The company) had some late-night charters that were due to come back and the gates didn't get locked (after) those charters returning. So the gate to the compound was open all night and there was no closed-circuit video available from that area."
Geurts said the company will talk today about whether security changes are needed.
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