Not sure of the downside of charging or not charging a NiMH. I hadn’t charged the one I had for two years. Put in the engine and it was found. Check it with a voltmeter first. 8 volts or above is Ok.
BTW the white batteries are NiCads. Same applies though. 8 volts or above is OK you won’t blow up the engine. Don’t use the charge circuit in the engine if the voltage is below 8 volts though.
Pete