Easy enough to fix.
Obtain recorders that record for the entire shift (10 hr battery life) that is rechargeable via battery swap and car plug in.
Require the officers to turn on their videos at the start of their daily briefing. Require them to turn in the video files end of the shift or failure to do so results in 1/2 pay for the day. Video files are evidence and failure to retain or properly handle or tamper with evidence shall be punished according to the applicable laws.
Loss or damage of the recorder requires the officer to replace the unit at his own cost which is deducted from his paycheck.
I would imagine the union wouldnt agree to those terms.