user38538: The project is to make a 4WD car using arduino uno(clone) and four toy dc motors. I am using a adafruit motor shield v1.2(clone). The car is required to run autonomously, please suggest batteries for the arduino and the shield.
Also when I am using external power connector for arduino, all the motors start at different timing.

user33045: Car batteries are wonderful, and almost never explode. A badly mistreated Li-{Fe,Po,Ion}, however... ouch. Otherwise use banks of NiMh/NiCd.
If you don’t fear death, use Li-Ion batteries with a TP4056 + DW01A IC, it can handle charging from USB, and provides over-discharge protection, so your batteries don’t die. 
https://www.addicore.com/TP4056-Charger-and-Protection-Module-p/ad310.htm
It also has current limiting built-in.

user20513: I've been using usb power packs.

Easy to source (can be found in all electronics stores and many general stores).
Come in many sizes (500mAh to 20,000 mAh are common).
Rechargable, usually by using a generic phone changer with a usb micro connector.
Not costly.
Quite roubust.
Most Arduino boards and many motor driver boards are designed to be powered from usb.

Make sure you get one that is rated for enough current for your project.

38538: <p>The project is to make a 4WD car using arduino uno(clone) and four toy dc motors. I am using a adafruit motor shield v1.2(clone). The car is required to run autonomously, please suggest batteries for the arduino and the shield.
Also when I am using external power connector for arduino, all the motors start at different timing.</p>
 33045: <p>Car batteries are wonderful, and almost never explode. A badly mistreated Li-{Fe,Po,Ion}, however... ouch. Otherwise use banks of NiMh/NiCd.</p>

<p>If you don’t fear death, use Li-Ion batteries with a TP4056 + DW01A IC, it can handle charging from USB, and provides over-discharge protection, so your batteries don’t die. 
<a href="https://www.addicore.com/TP4056-Charger-and-Protection-Module-p/ad310.htm" rel="nofollow noreferrer">https://www.addicore.com/TP4056-Charger-and-Protection-Module-p/ad310.htm</a>
It also has current limiting built-in.</p>
 20513: <p>I've been using usb power packs.</p>

<ul>
<li>Easy to source (can be found in all electronics stores and many general stores).</li>
<li>Come in many sizes (500mAh to 20,000 mAh are common).</li>
<li>Rechargable, usually by using a generic phone changer with a usb micro connector.</li>
<li>Not costly.</li>
<li>Quite roubust.</li>
<li>Most Arduino boards and many motor driver boards are designed to be powered from usb.</li>
</ul>

<p>Make sure you get one that is rated for enough current for your project.</p>
