Battery in paralle with circuit for uniterrupted power supply.

Thread Starter

Makis Germ

Joined Sep 7, 2015
Hello! I have a simple (maybe stupid) question. Can i just connect a recheargable battery in parallel with my 5V dc circuit in order to supply it for a very short period of time, in case of a power failure? Will this work? Why not? Is a more complex power circuit needed?


Joined May 3, 2013
There is no 5 Volt Battery.

Almost all the "5 Volt" equipment actually have a 3.6 Volt (1.2 Volt x 3 cells in Series) for normal working.
Since the AC power unit delivers 5 Volts, you just cannot connect the "battery" across the supply in a Floating mode - you will need to control the charging current..... etc.

Having said that, If you need a simple short term backup, you can use a Low Voltage Drop Diode to isolate the battery from the Normal 5 Volt supply (to avoid the 5 Volt charging the battery), and charge the batteries separately as and when needed.

This should work IF your 5 Volt equipment can work on 3.6 Volts (or 4.4 Volts in case of 2 Lead Acid Cells)


Joined Nov 4, 2013
4 nicads or NiMH cells will float at 5 volts well enough but at some point they would need to be kicked up to ~5.8 - 6 volts to recharge properly.

It's a poor power backup system but it would allow most 5 volt USB powered devices to run well enough being they are by design some of the more forgiving 5 volt powered devices around.