I have a battery that did service in my ZZR for 2 years, before giving up the ghost in that one. I then installed it in my ZRX where it worked fine for another 3 years.
A couple of weeks ago it started to hesitate, so I charged it up. At the same time I charged up a Motobatt battery that had failed to keep a charge in my ZZR about a year ago.
Anyway, today I rode the ZRX to lunch in Karagullen (WA), and all was fine. I left there around 1:30pm and paid a brief visit to Motorcycle Masters in Kewdale. When I wanted to leave there, the starter wouldn't turn over. I said "WTF" a number of times, but that didn't help. MM has a spare battery floating around, but that was not sufficiently charged to get me going.
Anyway, #2 son had to collect me, drive me to the city for urgent business as dictated by SWMBO, and then drive me back to MM.
He had brought with him the little battery starter pack that I bought a year ago and had never used. Connected, and it fired right up! Marvellous little item!
When I got home, I switched off, and tried to start again. No go. "WTF", I said.
I removed the offending battery, checked the voltage across the terminals (13.2V) and just for the hell of it, put the Motobatt (12.4V) in. Guess what? It started.
I guess the offending battery is simply rooted, or in layman's terms, it no longer works properly.