Hello,
If the user places the battery backward in the attached circuit, the batteries get very hot due to their high current.
To prevent that, I have added a diode into the circuit.

Here is my question in regards to diod.
1. Is using diode a good idea to prevent batteries from getting hot when they installed wrong?
2. If using a diod is a good idea, what type of through-hole diode do you suggest using for the circuit's power and current in the attached file???
3. If using a diode is not a good idea, what do you suggest to use to prevent the batteries from getting hot when they installed wrong?

Thank you for your help.

 

A diode is a good way to prevent reverse current if a battery is installed backwards.
A Schottky diode is good since they have a lower forward drop (≈0.4-0.5V) than a standard diode.

For minimum forward drop you could use a MOSFET which will have a drop consisting of its forward on-resistance times the current.
Since you can buy very low on-resistance MOSFETs, the drop can be in the tens of mV region for typcial battery load currents.
Below is an example circuit using an N-MOSFET:
Note that the normal current direction is source to drain through the MOSFET (a MOSFET can conduct equally well in either direction when it is biased on).
When the battery is connected in the reverse direction, the MOSFET gate-source is reverse biased and the MOSFET is thus off, blocking any reverse current.

 

Crutschow,
Many thanks for your response. My circuit has a 2 of 3.7V battery in series. Each battery has 3500 mah. Any Schottky diode could be used in this circuit?

 

Yes try 1N581x.. series..

 

Any Schottky diode could be used in this circuit?

It should be rated for at least 1.5 times the maximum battery load current.