Arduino Nano + SIM900 + Li-ion battery

Hello everyone,

I work for some time on a project.
The principle is quite simple: an Arduino Nano, two sensors, a shield SIM900 (this one) and a Li-ion battery.
The device must wake up 3-4 times a day max to transmit an HTTP request to a web server (if indeed the sensors detect a change in state).

I would like this thing to run for several days (or weeks?) without recharging so i try to make it energy efficient.

For this, I planned to implement a RTC module to generate interrupts (3 or 4 times daily max) and then turn on the SIM900 shield, launch the HTTP request and get back to sleep until the next interruption (powerdown mode) .

Meanwhile, for my first tests of autonomy I used the library Sleep_n0m1.h (Source). A request is sent to the web server every hour (sort of ping).
And as I still had no Li-ion battery on hand, I used a Powerbank (emergency charger for smartphone) 2200 mAh. I plugged directly into the USB port of the Arduino Nano: the module worked well, HTTP requests have been forwarded but it stopped working after 38 hours.

Once the Li-ion battery received (3.7V 5300 mAh), I wanted to connect to the Arduino Nano.
So I put a step-up 3.7V-5V to power the Arduino directly on his Vin. The shield SIM900 is powered directly from the 5V of the Arduino.
But there's a problem: the Arduino is powered, the shield power light is on, the network light too but this light goes off after a few seconds.
And the HTTP request is not transmitted.

So I suspect a power problem because when the assembly is powered via USB my PC, no worries either.
And I read on some forums that shield off automatically for safety if it is under- or over-powered.

Do you have any idea what I could do to fix this problem ?

Thanks in advance :wink:

So I put a step-up 3.7V-5V to power the Arduino directly on his Vin.

You are REALLY going to have to explain this.

TANSTAAFL. If you boost voltage, you decrease current, perhaps below what the device needs.

I've put a step-up between the Vin pin of my arduino and the 3,7v battery.
Well, maybe i'm wrong (i'm just an amateur), but if if power my Arduino with 5v maybe i could power my SIM900 shield with the 5V pin of the arduino ?
BTW, i'm probably wrong because it's not working...

I've put a step-up between the Vin pin of my arduino and the 3,7v battery.

I'm glad one of us knows what you are talking about. Just for the record, I know what an Arduino is and I know what a lithium ion battery is. What the heck do you mean by a step-up?

maybe i could power my SIM900 shield with the 5V pin of the arduino ?

The shield needs 2A. The Arduino can NOT provide 2A.

I'm sorry if i'm not clear, english is not my native language.
A "step-up" is a voltage boost regulator ; as this one : Pololu 5V Step-Up Voltage Regulator NCP1402
Maybe if i power the shield directly from this regulator, i could handle the 2A peaks ?

The available output current and output voltage ripple depend on the input voltage (see Typical Efficiency and Output Current section below), but the regulator can provide up to 200 mA if the input voltage is high enough.

You are not going to power a shield that takes 2 amps with a device that can provide 1/10th of that current.