user80887: recently in one of my projects I have wanted to make battery powered. I was wondering if I could connect the charger to the battery and the battery to the Arduino without blowing it. The battery is 12v 7.2 Ah and the charger is 12v 1 A.
(See attached)


user313: Just for clarity: your diagram shows the Arduino, the batteries, and the charger connected in parallel - which is correct for what you want to do. However, a 12v power supply (batteries, charger, or both) are at, or very close to the maximum input voltage spec the Uno. The Uno's voltage regulator has to waste - as heat - a good deal of power in reducing the voltage to 5v. And if the power supply provides any more than 12 volts, it will exceed regulator's spec.
Update:

how much do you think it would go over?

We can't know without knowing the specs on the particular batteries and charger. A battery charger has to apply a higher voltage than the present voltage of the battery it is trying to charge, in order to drive current into the battery against its (the battery's) voltage. You need to know more about the charger and the batteries.
Update 2:

The batteries are 12V 7.2 Ah and they are PK12V7.2 as the product name.

Those Lead/Acid cells. I didn't find a spec for the charger, but  in automotive use, Lead/Acids are charged at 14.2 volts. Your Uno's regulator won't like that. I'm guessing you measured your charger's output voltage with no load.
Try measuring it with the batteries attached and at low, medium, or almost fully charged. That should give you a better idea. We can only guess without the specs but it sounds like these components would be pushing your Uno's regulator pretty hard.
If these components and the Uno part of a system that requires 12v for some other components, I'd suggest using 2 power supplies, 12v for the components that need it, and 7 volts into Vin (or 5v, if well regulated, into the 5v pin) on your Uno. The lower voltage could be supplied by a buck converter powered off of the 12v, which would fairly efficient and require only one charger.

80887: <p>recently in one of my projects I have wanted to make battery powered. I was wondering if I could connect the charger to the battery and the battery to the Arduino without blowing it. The battery is 12v 7.2 Ah and the charger is 12v 1 A.</p>
<p>(See attached)</p>
<p><a href="https://i.stack.imgur.com/NVmWP.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NVmWP.png" alt="Schematic" /></a></p>
 313: <p>Just for clarity: your diagram shows the Arduino, the batteries, and the charger connected in <em>parallel</em> - which is correct for what you want to do. However, a 12v power supply (batteries, charger, or both) are at, or very close to the maximum input voltage spec the Uno. The Uno's voltage regulator has to waste - as heat - a good deal of power in reducing the voltage to 5v. And if the power supply provides any more than 12 volts, it will exceed regulator's spec.</p>
<p>Update:</p>
<blockquote>
<p>how much do you think it would go over?</p>
</blockquote>
<p>We can't know without knowing the specs on the particular batteries and charger. A battery charger has to apply a higher voltage than the present voltage of the battery it is trying to charge, in order to drive current into the battery against its (the battery's) voltage. You need to know more about the charger and the batteries.</p>
<p>Update 2:</p>
<blockquote>
<p>The batteries are 12V 7.2 Ah and they are PK12V7.2 as the product name.</p>
</blockquote>
<p>Those Lead/Acid cells. I didn't find a spec for the charger, but  in automotive use, Lead/Acids are charged at 14.2 volts. Your Uno's regulator won't like that. I'm guessing you measured your charger's output voltage with no load.</p>
<p>Try measuring it with the batteries attached and at low, medium, or almost fully charged. That should give you a better idea. We can only guess without the specs but it sounds like these components would be pushing your Uno's regulator pretty hard.</p>
<p>If these components and the Uno part of a system that requires 12v for some other components, I'd suggest using 2 power supplies, 12v for the components that need it, and 7 volts into Vin (or 5v, if well regulated, into the 5v pin) on your Uno. The lower voltage could be supplied by a buck converter powered off of the 12v, which would fairly efficient and require only one charger.</p>
