Is there any way a battery can charge other battery through isolated Charging circuit powered by a battery?

a battery charger doesn`t care Where it gets its power from, be it mains, solar or another battery, as long as it`s capable of supplying enough power, a regulator can be made to charge a battery from such supply.

Thanks YT2095,  I am thinking of developing a power supply that will work for a very long time if not forever when the components are capable of working forever, the system will involve 2x 12 volts batteries which could be of any amp, and 2x charger circuits, each of the charger circuit  will be simultaneously switching over in charging each other battery cells while both of them will power a load in a consecutive time, at this stage an MCU will be design with program to monitor ther charging period of one of the battery also enable the system to switch over the charger to the exhausted battery while the already charged battery will simutaneously take control of powering the same load.

I would prefer that each of the power charging source to be on battery, only not solar because I presumed that the solar energy will sometime become weak mostly at night time, the intension of this project is due to an interrupted power supply in a developing counteries or in a remote rural villages that never have access to their own National Electric power supply . What do you think about   this?

I think I understand, it`s basically a UPS, with a spare back-up battery, so while one is in use, the other is charging, and when charged it will swap over with the other battery to charge that.

I do something similar here in the Lab, only I took the internal battery leads outside of the UPS case, and swap the batteries manually when needed.

Yes it is similar function as the UPS, but the main technology invole is to electronically swap the battery lead to a charger circuit with the means of Microntroller to sence the limit in chargered current and simultaneously swap the charger circuit to the  empty battery, I also presumed that the both batteries will continually tied to the load in parallel connection, or will be a good ideal to interchange the Ouputs to a load?.

Best Regards.

If I were to do that, i think I would leave the GNDs (the - terminals) common, and just switch in/out the Positive leads, probably with power relays as a Flip-Flop arrangement.

your MCU would then only have to switch the base of a transistor to sink the current required for the relays at the right time (battery charged).

edited to add: Thinking about it, you probably don`t even need an MCU at all! if the relays have a set dropout voltage, you can simply set it such that when a battery needs charging it cannot supply sufficient power to a relay, the field collapses and automatically switches in the new battery 5086.contentimage_1.png

Your exact words describe a perpetual energy circuit, which cannot occur without getting energy from somewhere not mentioned.  Your exact words seem to say that you ruled out solar as the primary energy source for recharging what gets used by loads.  Was that really what you meant? 

It is possible to shuffle energy from one battery to another with a little bit of loss.  A tiny circuit which can move energy from a 1 to 2 volt supply such as one small battery to charge another 1 to 1.3 Volt battery is found in solar garden lights, to move power at 1 to 40mA from a 1 to 2 Volt solar cell to a small battery during daytime. Those also contain another power circuit to provide up to 10mA at 3V to a white LED while it is nighttime.

The circuits inside were globbed under epoxy, so I can't tell what was inside but I'll bet that they contain inductor(s), capacitors and a few transisters, possible similar to the Charge Theif circuit which got a writup online.

Those are much too small for serious power appliances but worth looking at if you are studying power management circuits.

Your exact words describe a perpetual energy circuit, which cannot occur without getting energy from somewhere not mentioned.  Your exact words seem to say that you ruled out solar as the primary energy source for recharging what gets used by loads.  Was that really what you meant? 

It is possible to shuffle energy from one battery to another with a little bit of loss.  A tiny circuit which can move energy from a 1 to 2 volt supply such as one small battery to charge another 1 to 1.3 Volt battery is found in solar garden lights, to move power at 1 to 40mA from a 1 to 2 Volt solar cell to a small battery during daytime. Those also contain another power circuit to provide up to 10mA at 3V to a white LED while it is nighttime.

The circuits inside were globbed under epoxy, so I can't tell what was inside but I'll bet that they contain inductor(s), capacitors and a few transisters, possible similar to the Charge Theif circuit which got a writup online.

Those are much too small for serious power appliances but worth looking at if you are studying power management circuits.