I've been using alkaline PP3 batteries to power my Nano based project while I'm developing it and getting through them at an unsustainable rate.
I know I could use a mains PSU, but batteries are far more convenient for me.
Most of the rechargeable PP3s I can find seem to have about 30% capacity of alkaline equivalents, and most are from brands no one has ever heard of, so I am not confident of their longevity.
So I'm wondering about getting a (nominal) 7v Lithium or NiMH pack.
Any thoughts on the best value for money (including a charger?)
If it is ok with 5V out you can use a standard power bank with an USB port, if your board don't have USB you can easily modify a standard usb charger cable to have just 2 wire + and - output.
It is also fairly easy to make your own bat-packs with 18650 batteries and a BMS board, both are cheap and easy to obtain and it's also easy to find guides to help you make it in a safe way.
USB power : no, because I'm using serial comms on the Tx/Rx pins and have run out of other pins (even with an I2C I/O expander), so the SoftwareSerial Library doesn't help.
5V phone charger : no, because, as I said, a battery is more convenient at the moment.
I don't think so, but to be sure you can just disable the 2 communication wires in i standard USB cable, leaving you with just the 2 power wires, gnd and +(VCC). A usb2 cable consists of only four wires; VCC, Data-, Data+, Gnd.
Just tried it with an unmolested USB cable and my daughter's USB battery pack. Initially it seems fine, but about 15sec after I connect to the Nano with Bluetooth (HC05 using serial comms on Tx/Rx) either the battery or the Nano seems to shut down.
Is that likely to be fixed if I cut the data connections in the USB cable?
The USB charger has detected that not enough current is being drawn by a charging battery. First try turning on the MCU's LED to see if the current increase keeps the charger on. If that don't work, use a LED and resistor across the supply.
Pin 13 is tied up as an output to a piezo transducer ... so that would get annoying.
There's also an I2C 16x2 LCD (with LED backlight), an I2C IO expander and a HC05 bluetooth transceiver, all powered via the Nano's 5v and 3.3v pins, so I'm not convinced one extra LED will make the difference.
You might look for an "18650 Battery Shield V3". It is a battery holder with a charger with protection, 3.3V linear regulators, and a 5V boost converter. You would need one of those and an 18650 lithium battery, The battery doesn't need to be protected, but will work ok if it is. It's not intended as a powerbank, so you shouldn't need to draw any minimum current to keep it turned on. These are widely avaliable. Here's one at Banggood:
