we use GPRS shield v1.0 ( 1 pcs ) and v1.2 ( 2 pcs ) and found now that measurements with arduino uno on Ain4 and Ain5 are wrong or 0 depending on modem status.
acc. WIKI
GPRS Shield doesn’t use I2C port, you can disconnect the connection from SIM900 I2C port to A4/A5
we would like to do that, but dont know how to disconnect?
cut ?what? leg of the modem chip?
pls help us.
Hi , for GPRS Shield v1.2 , you can cut the wire that at the red signal place by a knife.
For GPRS Shiled v1.0 , you can ignore the issue since the A4/A5 doesn’t connected to SIM900 
Deray
thanks for the help, very good service!
i hope next revision has jumpers for that issue.
other question, i dont know the status of the RTC usage, but getting the mentioned type of battery
take me 2 month, with prices between 3USD and 7USD. could you use a battery holder for batteries we get in the supermarket ( or supply the battery with the board )?