user43037: I've recently started tinkering with Arduino, and I'm attempting to build a little 2WD robot based on an Arduino Nano.
I was thinking of powering the robot using two 14500 LiFePO4 batteries, which I understand will fit in a standard 2 x AA battery holder, and in series will give me about 6.4V, which should be ideal.
If I were instead going to use AA batteries, I think I'd need 4 of them, which will make my robot a fair bit bulkier.
I would like to be able to charge the batteries simply by plugging a standard USB cable into the Nano's USB socket.
Is there some easy way to safely do this? Do I need a separate charging module board, or is there some way to do it directly from the Nano?

user4143: No, you cannot charge a Lithium-Ion battery (of any variant) directly from an Arduino. You require a Lithium-Ion battery charge controller. 
The best source for these kinds of things at a small size is retailers of model vehicle parts.

43037: <p>I've recently started tinkering with Arduino, and I'm attempting to build a little 2WD robot based on an Arduino Nano.</p>

<p>I was thinking of powering the robot using two 14500 LiFePO4 batteries, which I understand will fit in a standard 2 x AA battery holder, and in series will give me about 6.4V, which should be ideal.</p>

<p>If I were instead going to use AA batteries, I think I'd need 4 of them, which will make my robot a fair bit bulkier.</p>

<p>I would like to be able to charge the batteries simply by plugging a standard USB cable into the Nano's USB socket.</p>

<p>Is there some easy way to safely do this? Do I need a separate charging module board, or is there some way to do it directly from the Nano?</p>
 4143: <p>No, you cannot charge a Lithium-Ion battery (of any variant) directly from an Arduino. You require a Lithium-Ion battery charge controller. </p>

<p>The best source for these kinds of things at a small size is retailers of model vehicle parts.</p>
