Only post I saw related to this is 10 years old with no replies so thought I would give it a shot. I absolutely have the worst luck with the Odyssey batteries in my 7A. I am lucky to get 2 years out of them. A friend recommended the Antigravity Lithium battery. Anyone else have experience with these? If not is there another recommendation to replace the Odyssey?
I used the PC680 for a number of years with decent results. They, others don't last forever and even the slightest drain can ruin them over time.
Obviously, if there is ANYTHING that uses ANY electricity when the "MASTER" is off, you need to remove it for now.
A friend of mine was having trouble with his RV14 (390) cranking slowly and then "crickets", no crank.
Since I changed to the EarthX LiFePo batteries back when they first came out (and even did some testing), I have been using them since then. Initially, the "680 equivalent" fit rather "snug" in the PC689 battery box. THey have since shave a few millimeters off the case and it drops in quite easily. Their "900" is in the same case and does so as well.
So naturally I suggested that my friend get an EarthX. He got the 900 for his RV14.
BUT!!!!!!
Before we installed the new battery, we checked and found a few things.
1. The GROUND cable, where connect to the engine block was NOT as tight as it should be.
2. We REMOVED the cable and discovered that when his engine had been removed, enhanced, and returned, there was ***PAINT** left where the ground connected.
These two items could have led to a) poor ability of the PC680 cranking as it should and b) less than proper voltage to the battery for charging.
I would guess that your current PC680 is "toast" as far as aviation is concerned. Don't sweat it. Don't look back. Just replace it NOW so that you don't get stranded. (My buddy picked up a kid at my hangar and took her flying for a while. They returned to my hangar and when he got in his plane to taxi to his hangar, it would NOT start. It happened that quickly. Luckily he was not off somewhere so we just pulled it in, got the EarthX and installed it.
He is now a happy camper.
A new EarthX ETX680 will spin the engine a LOT faster than a new PC680. It will also suck a lot more amps from your alternator to replenish what was removed for the cranking. So make sure that you have a good one. If you have a 50A alternator, don't be surprised to see 55-60 amps for a minute or so. And if you want more capacity the ETX900 will fit the same space (yes, your wallet will be a little lighter
).
One more thing ...
Depending upon where your battery is mounted and depending upon your current CG, be very mindful that the EarthX is SHOCKingly much LIGHTer than the PC680 (or its equivalents).