Rechargeable Battery Use

[Rod]

A couple of years ago we had a “hole in the wall” gas fire installed. It’s controlled by a remote handset and there were two options for the fire, mains controls or battery powered controls. As it was mainly for emergency use we opted for battery power. The remote and fire controls “talk” to each other but sadly it “eats” batteries, 3 C type every couple of months.
Would it work if I replaced the batteries with rechargeable ones continuously topped up with a suitable charger?

Rid

 

[9fingers]

A couple of years ago we had a “hole in the wall” gas fire installed. It’s controlled by a remote handset and there were two options for the fire, mains controls or battery powered controls. As it was mainly for emergency use we opted for battery power. The remote and fire controls “talk” to each other but sadly it “eats” batteries, 3 C type every couple of months.
Would it work if I replaced the batteries with rechargeable ones continuously topped up with a suitable charger?

Rid

A quality C cell is capable of delivering about 8mAH so if you are only getting 2 months that is suggesting your device is drawing an average of 5mA which is absolutely appalling for a battery power design modern design.
We have to assume that it is functioning as designed.

The problem with replacing dry cells with rechargeable is the terminal voltages don't match.
Dry cells new will deliver in excess of 1.5volts maybe 1.6v so three will give up to 4.8volts.
The end point of dry cells is 1 to 1.1v per cell -lets say 3.3 volts for 3.

Nicads or NiMh range from maybe 1.3v to 1.1v so even fully charged, the best voltage you can expect is 3.9v well down the range of the dry cell pack.

If the design is poor in terms of current, it is probably not got brilliant voltage tolerance either. I appreciate you intend to charge it continuously but that is not the best regime for rechargeable systems other than lead acid which is why they are used for back up in alarms and UPS applications.
Lead acid at 2v per cell nominal don't sit comfortably with your supply range either.

My solution would be to fit a capacitor instead of one of the cells( Say 1000uF at 10v or more) and drive it from a 5v USB wall wart or one of those 13a sockets with USB chargers built in which would be neater..

Your circuit must be tolerant of 3 new top voltage dry cells and so it is almost certain to tolerate being run from 5v. A series diode ( 1N4000 series) in the battery box too will drop around 0.5 volt which should do the job nicely.

Bob