Oregon Rental company trying to charge me a crazy fee

[green2man0]

So my question is: We had our annual inspection Mid November. A day or 2 before the inspection our smoke detector starting acting up (would go off every time we opened the oven) so I pulled the battery and put it on my multimeter (was bad)(detectors are hardwired into the house) they came did the inspection and I replaced the battery that evening. I got a letter a couple days later stating they were charging me a 250$ tampering fee for changing the battery...Both the battery and cover were sitting on the on the dresser in plain view. I called the rental company and explained the situation...I've only been able to talk to the secretary (some 20 year old girl who has been working there a few weeks)(And left messages with the manager/agent) They are very unpleasant to deal with. We have been in the residence for 2 years and have never been late on rent. House was built in 2003 +-1 year. It feels like I'm being extorted...The follow up letter I received stated that if we refused to pay they would void our lease. I've talked to a friend of ours who is a business lawyer and she did not know all the details about Oregon rental law so I figured I'd ask here. Any help would be much appreciated.

Thanks,
Aaron S.