I had to replace my battery the other day. The solenoid was making the classic "ticking" sound when trying to start, no juice. I have a home battery charger that couldn't make sense of its state and it finally gave up trying to charge it. I had them test it exhaustively at the auto parts store and it had a completely dead cell. The car is CPO and had a Lexus-branded Mexican-sourced unit, but oddly no date code was punched out on it. I think it was just junk.

The interesting thing to me is that I'd been noticing what I now realize were weak battery symptoms since I bought the car almost two years ago. Cranking always seemed just a tad slow, but it continued to start OK within a few turns so I didn't pursue it. A good reduction gear type starter can spin up the engine with relatively low current and is able to start anyway; the battery had probably been failing for a long time and was borderline dead, but even so the starter was able to make the most of it. The only bad part about that is you can't really judge the margin - one day it'll spin right up and the next it just won't start. The new battery does spin the starter decidedly stronger than before, and the power door and trunk closers seem happier when activated when the car is off.

It's a good thing it never stranded me anywhere. The lesson learned for me was to pay more attention to the battery's health, even if the car never fails to start. Batteries are cheap, take all of five minutes to install on this car, and don't last forever.

 

Another problem with a battery like that is that it puts a temendous load on the alternator and I have had one go bad by having to constantly put out max amps trying to charge a marginal battery over time.