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Murphy’s Law with my OBD2 reader
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edy:
Thanks everyone for all the suggestions.

I just took the car out for a quick run from work to the bank (3 minutes away). I had the battery negative disconnected from the car negative lead during the entire whole morning (9:30am-1:30pm) since I parked at work (at 9:30am the battery was 12.43V after disconnecting). Checked again before starting the car (1:40pm), battery voltage was relatively stable at 12.38V.

Started fine, drove to the bank, stayed there maybe 10 minutes and drove back to work and got back around 2:00pm. Drive each way probably less than 5 minutes. Once I parked at work again (2:00pm), I checked the battery after I disconnected it again at negative terminal only and was getting 12.52V. I've left it disconnected for now. I will check battery again when I finish work closer to 6-7pm. Again I am going to assume some "settling" is normal as it just stopped charging and will probably drop a bit over the next few hours before I leave work.

I'm going to try this again over the next few days, always disconnecting the battery whenever I park, and keep checking the battery voltage. If it is charging when I am driving (which is suggested by the fact that it was 12.38V at 1:40pm and by the time I got back after driving at 2:00pm it was 12.52V) then the alternator must be doing the job. If the voltage remains stable when parked, that is good news for the battery. Remember, with the battery disconnected it only dropped from 12.42V to 12.38V over 4 hours this morning. I am also accounting that there may be measurement variability, temperature changes due to hot engine compartment, and "settling" after being charged while driving.

Therefore the last possible culprit would be when the battery is connected to the car, probably some parasitic current draw in the vehicle when it is parked... perhaps not constant, it may be sporadic. Then I have to isolate what system is responsible for it. For now, I'll continue keeping the battery disconnected whenever parked and will make a log of voltage each time I connect and disconnect the battery (when starting and parking the car), along with times and temperatures, and post the results.
sokoloff:

--- Quote from: edy on January 10, 2023, 07:09:10 pm ---If it is charging when I am driving (which is suggested by the fact that it was 12.38V at 1:40pm and by the time I got back after driving at 2:00pm it was 12.52V) then the alternator must be doing the job.

--- End quote ---
Why not directly measure that by starting the car and measuring the voltage at the battery terminals? If it's over around 13.8V at just above idle, you're probably good. (It should be closer to 14.2V at a normal RPM, but if it's noticeably above the resting voltage, it's charging [or offering charge at least].)

You could have a failed diode in the alternator's rectifier or worn brushes that would allow partial operation but still indicate the need for an alternator replacement. Unfortunately, on the CR-V, they're in a somewhat inconvenient location. It's DIY-able, but is more annoying than most, especially the bottom bolt.
themadhippy:
could it be as simple as your not driving the car long enough to replace the  starting current.It used to be said it takes 20 minutes of average driving to replace the energy taken by the starting motor,longer if you had the headlights on,or windscreen wipers going
tom66:
Worth also checking the starter motor itself.  When the starter motor in my 206 was going out, it would take sometimes 10 seconds to get the engine going.  A brand new replacement had it running in one second.  Combine that with a weak battery and perhaps it just doesn't have the oomph required to turn the engine over fast enough to guarantee start.
edy:
I checked the battery last  night and this morning. When I parked the car again around 2pm yesterday it was at 12.52V (having just been driven). Left from work at around 7pm and before I hooked in the battery again it was at 12.39V (note: battery not connected to car from 2-7pm). Drove home arriving 7:28pm, checked battery and was 12.53V (having just been charged by alternator while driving). Unplugged battery again overnight, but checked in again at 10pm last night and it had settled to 12.40V after several hours.

This morning checked battery and it was 12.31V (temperature -7C outside). Started fine, drove kid to school then work, about 40 minutes drive. Got to work and unplugged battery and it was 12.18V! Keep in mind that due to cold mornings, I start heater in car and have radio going and perhaps not driving long enough (and if battery is already "meh") then perhaps all these short trips and cold weather is contributing to the problem on top of an already questionable battery.

My 2011 Honda CR-V has only 80,000km on it (50,000 miles) which is a joke for an almost 13 year old car. Most trips have been short, school and work are 10-15 minutes away. Only when I need to drop kids and then go to work I need to do a longer route. Combined with cold temperatures, running a bunch of things in the morning (heater/radio,etc) and a battery that is showing it's age, plus other factors that may be compounding an already compromised system takes it over the edge after several days like this.

I found this post and going through some of the suggestions and testing, as well as comparing to the voltages I'm getting:

https://www.jdpower.com/cars/shopping-guides/how-to-test-a-car-battery-with-a-multimeter

I checked voltage on battery terminals when hooked in and car started, to see what alternator is doing. I'm getting 14.10-14.20V, especially if I rev up the engine a bit and everything is off. Once I start turning on a bunch of stuff (lights, heater, radio) it drops to 13.89V. But according to the article above, anything above 13.5V is still ok, so I don't believe alternator is necessarily to blame. As well, once the battery has a charge, the starter turns over the engine in less than 2 seconds.

I also turned-over the car while trying to read battery voltage while starter was cranking. Keep in mind after all this testing with all accessories on while parking, the terminal voltage on battery had dipped to 11.93-12.00V but I was still able to turn-over the car and for a brief moment I could read the voltage went down to about 9V while starter was drawing power, but I can't be sure (my multimeter doesn't update very fast).

When I left the car this morning at 9:04am it was reading 11.93V. I'll see what happens tonight. I left battery unhooked from the car and will test it again when I leave work. Trip home is only 10-15 minutes (4.5 miles city). Likely not enough to charge my battery much either, but I'll leave it unplugged again overnight and check again each morning.

I'm suspecting it's just a weak old battery that coupled with perhaps some of the usage patterns and contributions from older alternator/starter is starting to dip below reliable cranking power necessary in the cold Canadian mornings, despite having been tested twice at Canadian Tire (using their "fancy" battery testing gear) claiming it's still "ok". Maybe I need to increase my trip time and reduce the use of interior accessories, heater, radio and lights completely to balance out.
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