Its been some time, but it seems I toasted my first battery on this trimmer. A couple weeks back I went to use it and it didn't spin up. I pushed the battery indicator button on the pack (shows red/orange/green light for charge status) and I got nothing. I plugged it into the charger, I got an error and it wouldn't charge. I have yet to do anything further, but it seems that 5 years is what I got out of the first pack. Not too bad, but I'd be lying if I said I was a bit disappointed. Thankfully, it seems other companies now offer aftermarket packs for the Ryobi 18V tools. A replacement isn't horribly painful. I think I paid about $120 for the trimmer back in 2010. Back then a new pack was either $75 or $90. Now, you can get an aftermarket one off amazon for $40 with a bit larger battery. A Ryobi brand pack is $50.
However, before I replace the pack. I think I will give this a go:
Cell Re-balance of Ryobi One+ 18V Li-ion Battery