Interested to learn if this is a bad idea and why.
I have battery powered wireless doorbell receivers. They run on 2 AA batteries (e.g. ~3VDC with alkaline or 2.4VDC with NiMH). The problem is that every time the batteries run out I have to do a little "reprogramming" dance after inserting the new batteries.
Since these receivers are stationary and near outlets I figured I could just take the batteries out and solder in a 3VDC wall-wart supply.
However anytime these are unplugged or there is a power outage, they would need to be reprogrammed.
So I was thinking...if I leave the Alkaline (or NiMH) batteries in there then theoretically the wall supply (3VDC) being higher...the batteries wouldn't discharge unless unplugged...then they would function as a backup so I don't have to reprogram the bell if I unplug it temporarily.
Originally I was thinking of just leaving the NiMH in there since they are rechargeable anyway...but with a constant 3VDC applied to them it might kill them in short order (would require some type of charging management circuit I guess)?
Then I was wondering what the consequence would be if I left alkalines in there (low self-discharge compared to NiMH). Their full voltage should be around 3VDC...but if they discharge a bit then their voltage drops off pretty quickly and I am not sure what happens at that point if they have 3VDC applied across them.
Interested to learn as well as have recommendations about what to do or not do here. Thanks.