hi.. it, sounds like the battery yes,,, but check the water in the cells first BEFORE you take a charging....
I can told ju ,,, My battery in my -93 LS 400 do I change last year,,, it, was the originabattery from the factory,,,, 11 Year... in the cold sweden...:)
The warranty at the battery from Toyota/Lexus,,, is 8 year... here in sweden!
in the swedish eastcoast is it now,,,, about 15-18gr... Celsius,,, ***** the autum is here soon,,, :(