Thanks, sorry more questions, as the 12 input would have to have the same connection as the external, is it best to put another socket on the gas analyzer, the original for powering the unit, externally, just in case my added batteries fail and an extra 1 to charge the 18650, the out put of the boost converter what is best there, a diode or a switch to stop the 12v back feeding if used on external power and last, the 12v 1S charger with 2 batteries, why a 1S and not a 2S



Thanks again

 

I would use a DPDT switch. In battery mode it would connect the jack + to the charger input and the converter + input to the battery +. In external power mode it would connect the jack+ to the analyzer + input and disconnect the + input to the converter. The advantage of this arrangement is that when it is switched to external power, the battery is disconnected from the converter so it will not discharge through it when not in use.
Regards,
Keith

 

does no one know or have I done something to upset you all?

I was not upset, I just had nothing to say.