How much power for GSM modem via lithium batteries? Mess up code != enough power

Using Arduino General Electronics
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So, I'm trying to use my uno + arduino GSM shield on standalone power. Combined, I have over 8,000 mAh available, over ~5 volts or so.

My code works beautifully when it's plugged in.

Problem: Using standalone lithium batteries seems to mess up the code / GSM modem because there is not enough power. It happens after an hour or two.

Any advice on what I can do here? What are my actual options?

Things tried:

  1. Getting bigger batteries. Doesn't seem to matter much.

  2. Using power management options like lowpower.h library for the uno, and turning off the GSM when not in use (99%) of the time.

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shadybrady55:
So, I'm trying to use my uno + arduino GSM shield on standalone power. Combined, I have over 8,000 mAh available, over ~5 volts or so.

is it 4.5V, 5V , 5.5V, 6V..... ? ~5V or so is not a value
which batteries? how are they 'combined' ?
how is your arduino powered ? (where do you put your ... "~5 volts or so" ? )

My code works beautifully when it's plugged in.

again.... what does that mean ? plugged in what ?

Problem: Using standalone lithium batteries seems to mess up the code / GSM modem because there is not enough power. It happens after an hour or two.

what happens exactly ?

what is the battery voltage when it ...'happens' ?

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