Yesterday morning, my GC would not start, the engine barely turned. I cleaned the battery terminals with baking soda and a brush, charged the battery and it started numerous times the rest of the day. I took it to the local auto parts store where they tested the battery (3 years old) and said it’s good including the alternator which was replaced 6 months ago. This morning; same problem.

 

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Those hand-held AC conductance meters are handy to provide a quick check on battery health.

My old-school mind prefers actual testing to the specification.

To properly test the battery, first ensure it is fully charged, to 100% state of charge. Use a correct / appropriate charger and charge for 24 hours. Then, allow to sit idle and disconnected for 24 hours. Connect a volt meter. Connect an adjustable load. Connect an ammeter. Set the load so that it would deplete the battery in 20 hours, according to the nameplate rating, a 100Ah battery would have a 5A load applied, 100Ah/20h=5A. Measure the run time in hours.

A battery is considered usable when the actual capacity exceeds 50% of the nameplate rating.


An easy first step is to measure the battery voltage. A fully charged idle battery should be 12.5 to 12.8 VDC, depending on the battery chemistry and the ambient temperature.

What is the measured battery voltage?

 

It would be helpful if you check to see if something is running the battery down from a constant draw on the electrical system. Did you clean the battery grounds, it could be not making a good connection and charging isn't keeping up.

Battery cables also go bad inside the outer shield that causes a lot of problems and not easy to find. I found a bad one when I replaced them with HD ones because of larger alt. that I installed. When I pealed the cable back it was really bad about 2-3" in from battery terminal.

 

I keep my dash cam plugged in 24/7 to the always-powered cigar lighter socket; never been a problem before. Since my battery is 3 years old, I figured it's best to buy a new one and will monitor what happens. Also, the positive and negative cables are as old as the vehicle (2000), I should replace them. I cut off an inch of cable to where I saw shinny copper.

 

..and let's not forget the battery temperature sensor, the button shaped thingy in the center of the battery tray. One of those got me chasing my tail (electrically speaking) in my dear departed '99 Cherokee Ltd. If the sensor begins to fail it will negatively affect battery charge system functionality (i.e., become resistive). It can be elusive to detect due to variability and or intermittent nature of failure modes over temperature.