I have a GE security system, Simon 3. I want to position the system so
that it runs somewhere between 20 - 30 days without electricity. The
internal backup battery will allow it to work 24 hours without
electricity. By it, I am exclusively taking about the main panel.
Given the
specs as noted in the link below,  what would be some options for this
to happen. I was thinking a pre-charged UPS system (UPS), but I am not
sure if one that exist that will keep is powered for 20 - 30 days.

I am looking for back up battery solutions that will cost less than
300. And doesn't require any intervention during that 20 - 30 day
period.

The specs of the system are
http://www.gesecurity.com/portal/GESDownload?ID=94&DID=841&documenttype=Data%20Sheet

The built-in backup battery is 6v, 1.2 AH & provides power for 24
hours.  For 30-day backup, use a 6 volt battery rated at 36 amp-hours
or higher.

A 6-volt lead-acid marine battery, with a simple charger, should do
the trick, with an expected life of 6 years or greater.  6-volt
lead-acid marine batteries and chargers are available from suppliers
of photovoltaic solar cells for off-the-grid households.

I am not a technician at all. Where could I find something such as
that...Would it fit the price range i noted.

My husband is a registered professional engineer who used to operate a
business selling high-end security systems. His experience with marine
batteries was not good; they needed frequent servicing, and sometimes
set off "low battery" signals which the system reported to the
monitoring station. After the "low battery" episodes, the system often
failed to recharge the battery adequately.

OK, here's another possibility.  Purchase an after-market car alarm
($100) and a 12V car battery ($60).  The car alarm will have
connections for "pin switches" "vibration sensor" etc. intrusion
detection.  To recharge the battery, simply connect it to your car via
jumper cables each month, and run the car engine for an hour or so.

The reliability characteristics of this system are well known, since
millions have been in use worldwide for the past 20 years.  For
example, I installed one of these in my Honda Civic in 1993, and it's
performed with absolute reliability over the past 16 years and 5,000
open-close cycles of the car door (pin switch):  zero false alarms. 
Car battery is replaced every 8 years or so.

You have said yourself that you are not a technician. Unfortunatively,
you cannot replace your current battery inside the UPS unit with one
with a might higher capacity. The UPS simply would not be able to
recharge such a big battery.

Also unfortunatively, such dedicated and uncommon systems are much
more expensive than usual UPS systems.

Therefore, you can either buy a very expensive device or completely
make one yourself. In this case, you would have one large battery or a
bank of batteries. You will buy a car battery recharger separately as
well as a DC-AC converter that will convert 12 V DC to 120 V AC.
Converter should be sine wave and not square wave or "modified sine
wave" unit. Low voltage alarm would either exist on the converter or
you would have to buy a separate gadget for that, too...

You can buy big 6 volt batteries at Sam's Club (Golf cart stores, boat
and RV stores) for about $60 perhaps as much as 200 amp hours. Ask
Sam's to charge the battery for you. Connect this battery to the
termials of the 24 hour battery with light duty wire, positive to
positive; negative to negative, much as you would jump start a car. In
theory the amp hours are good for 6 months, longer, if the circuit in
the alarm keeps both batteries charged. You may need to clean the
teminals monthly to insure a good connection.   Neil