2 days ago I was sitting in a parking lot on a phone call, engine off but acc was on and fan was blowing, radio on, phone charger plugged in, for prob 25 mins or so. Went to crank it up and it wouldn’t start. Blamed it on myself for losing track of time with the important call I was on, got jumped, drove home with headlights on just fine. Dash read 13v most of the way, sometimes would be 14v. Drove home 15 mins, parked it and turned off, then cranked it 2 times to see if all was still good and it was fine. To be safe, I put my battery tender on it overnight and by morning the light was green.
Yesterday I hopped in to go take care of some things around 5pm. It cranked up fine, ran fine, and I drove probably 50 miles and engine had been running for almost 2 hours straight at this point. I got to a gas station and shut it off, cranked it up 5 mins later and was perfectly normal. Got home around 8, parked it for the night. Again everything yesterday was 100% normal both starting and running. Dash was consistent at 13-14v.
Today, went to start it around the same time (5pm) and the battery sounded noticeably weak, but it started the engine. I pulled out the driveway and went to accelerate and it wouldn’t go up past 1800 rpms and was extremely erratic with the gas pedal responsiveness. I pulled over and let it idle for awhile thinking maybe the battery was in fact bad after all and just needed to charge back up to get me running normal again so I could go get a new battery, but after 20 mins of running the engine it still acted the same. Even in park or neutral if I floored it it wouldn’t go above 1800 rpm’s and was still very erratic, felt and drove the same way it would if I was running out of gas (definitely am not) and hoping to make it home. The dash said 13v the entire time during all of this, and even 14v occasionally, but also dipped to 12v a time or two when I turned the ac and lights on to “test” it. Got home and turned it off, then tried to crank it back up (thinking maybe it was in some weird limp mode and needed to be reset) but it wouldn’t crank. Voltage on dash was 10-11v.
Anyway, no dash lights have come on throughout this entire process at any time. Does this sound like a bad battery that won’t accept a charge or a bad alternator? And how would you recommend determining which one it is considering I can’t take it in anywhere (unless I fully charge the battery and hope for the best)? Also I don’t fully trust those auto part store testers, they are far from accurate.
Any input is welcome. The battery is one thing but the super rough running when accelerating has me concerned more now. My old Tahoe would throw a code on the dash when it was in limp mode, but as mentioned zero dash lights at all in this process.
Also battery is “ultra start” which I’ve never heard of and has a sticker with Jan 2020 punched out, and another sticker that says 18 mos (warranty period I’m sure). So it’s definitely overdue for changing but how common is a bad battery to not accept a charge from a good alternator and also cause running/peformance issues ? Where would you start if this was your truck dead in the driveway with the hood up?
