Thoughts on my strange service experience?

At about 92k miles (2 months ago), my 2005 Prius started having a battery issue... When going about 40 mph and above and not having to stop or apply my brakes, my battery would drain (to just 1-2 bars) in about 5-10 minutes and not recharge until I got into stop-and-go traffic (this would happen about 9 out of 10 times). Mpg was still pretty good during that time, but when I finally had to stop, the engine had to kick on to recharge the battery and my mpg just sucked...I went from averaging 45 mph to 39 mph.

I took my car into the dealership for them to have a look and to also perform my 95k service. When I told them that I feared the battery was dying, they said that the good news was that I had another year on my warranty (not sure if the battery warranty is extended in California). The service advisor eventually came back and stated that they had also observed the battery charging problem and that they had to pinpoint the exact problem (either an igniter, a battery cell, or something else that I can't remember). They even started the process of getting me a rental car for a couple of days. However, the service advisor then came back and stated that no problem was found...he even walked me back into the garage where they were working on all of the cars just to ask the technician working on my car if there was a problem...he also stated that no problem was found. When I asked how initially a problem was found and then suddenly not found, I really didn't get a straight answer (I should have pressed harder). Anyway...after 10 hours in the shop, they pulled my car around and the manager came out to speak to me...stating how the 95k service showed no problems and how no problem with the battery was found. When I asked about how to prove to them that there really was an issue, he stated that if the problem kept occurring I could bring it back in and they could have one of their tech leads drive it home for the night as kind of a road test.

It's been five days now and guess what? The battery issue has not resurfaced. I'm totally confused... Could the 95k service somehow fix the battery?...I doubt it. Did they do something behind the scenes and not tell me? If so, why? Any thoughts that anyone might have would be greatly appreciated. I guess that I should be happy; however, I keep expecting the problem to resurface any day now...

 

nh7o:

Thanks for your detailed information...it's really useful. Based on what you said, my guess would be that they ran a test prior to the 95k service and saw the battery drain like I did. Then...perhaps something in the 95k service (standard service + oil conditioner and fuel system cleaner), resolved the problem. Not sure why they wouldn't just tell me that though. I have taken a couple of 60+ mile drives since then and the battery charge is mostly staying at 6 bars (and occasionally going to 7, which I hadn't seen in a while).

uart & bisco:

I bought this car new in 2005...no battery drainage issue until about the 92k mark. Sometimes the battery drain occurred during the initial 5-10 minutes of the drive and sometimes it didn't. I typically drive it to a from work which is 11 miles away. I go to work on the highway with just about 1/2 mile on either end of the trip on city streets. The battery would go to 1-2 bars usually at the last 1-3 miles on the highway drive. So...in this situation, it occurred within the first 10 minutes of the drive. From work to home, I take city streets...mostly 40-50mph roads. I was always good for the first few miles (a lot of stop and go), but then I would hit a 4 mile 50mph stretch of road. If I made all of the lights, 9 times out of 10 my battery would be a 1-2 bars just before the end of that four mile stretch. I'd say that this would be 12-15 minutes into the drive. When functioning correctly (or what I believe to be correct), I do typically set a 1-2 bar reduction in the first few minutes, but then the battery charge typically goes quickly back to about 6 bars.

 

The problem started pretty suddenly a about two months ago...I just suddenly started noticing the engine kicking-on at times that it never had before (I have been going the same route to and from work for years) and my mpg dropped by 4-5 mpg in no time. No check engine light or anything. I forgot the mention that turning the AC on just killed the battery charge. I had to use the AC in 100+ degree heat one day for about 20 minutes...the battery quickly went to 1-3 bars and stayed there (mostly in stop-and-go traffic) until I was able to turn the AC off about a mile or so away from home and it went back to 5-6 bars. Anyway...like I said...it seems okay for now. Sure would like to know exactly what had caused the problem and how the 95k service managed to resolve it (at least for now).

 

The onset of this problem did not correspond to the start of seasonal AC use...in fact, I've only used the AC once this spring/summer (a couple of weeks ago). It's just that the one time I used the AC, the battery drained much quicker and would never recover until I turned it off.