Having an odd issue with DS1307, when battery is applied (CR2032 3V battery with 3.44V coming off of it) the RTC will not respond on I2C, though I can see the oscillator happily ticking away on scope, I can see the data and clock coming from the AVR, but it refuses to give any data out, however remove the battery (let that pin float), and it will respond properly to I2C, and never even loses time, any ideas? I have checked and all polarities are correct, quite baffling! Infact it even keeps time off of the battery, but I have to remove the battery first while powered up to get the time again.
Nevermind I figured it out, turned out my USB was only supplying 4.21V which was low enough to trigger the DS1307 into battery mode, hooked it up to an actual 5v supply and all is well.