Minty Boost vs 9V as Arduino Back-Up

[HooctAwnFonix]

I want to put a back-up battery on an Arduino project and I'm wondering if I really need a Minty Boost.

The pros of the Minty Boost would be, A) it will last longer, B) it won't get drawn on at all until DC goes out, C) it looks good!
The cons are that it costs me $20 instead of $1.50 with the 9V battery...

And just to make sure I understand, if I use a 9V battery in parallel with a 9V DC supply, will the battery not get drawn on (or very little) until the DC goes out? I think that this may do the trick since all I want is ~10 mins of survival after DC goes out.

[Donziboy2]

The minty will draw power if it is plugged into batteries, not much but some. And your right it is an expensive backup system.
How much power are you drawing?
Im not sure how backup batteries in devices react to DC supplies. Im sure it would depend on the batteries internal resistance.... If the supply voltage is higher then the battery, current will flow. Im thinking put a diode on the battery to prevent current from being pushed into it but i could be wrong.

[adafruit_support_bill]

You don't want to connect the minty in parallel with another regulated supply. One of the regulators will end up doing all the work. If it is the minty, your batteries will be drained quickly.

[HooctAwnFonix]

I was thinking of using the Minty on the USB of the Arduino - I've read that it switches automatically the USB when the power supply goes out. I'm just trying to figure if I can do this 10 minutes of back-up more cheaply by putting a 9V battery in parallel with a 9V power supply.

[adafruit_support_bill]

The 9v with a diode in series should work. That would be the cheapest solution. As noted in a previous response, the minty has an idle current of a couple mA and will slowly drain the batteries.

[ocb]

I did a similar thing, putting a 9V dry battery parallel to a 9v supply.

After a few days the dry battery was completely dead.