It used to be that you could measure battery voltage with a meter, and see the current voltage, the drop in voltage as it was cranking, then the increase in voltage when the alternator came up in rpm- even at idle. The only thing you couldn't tell easily was whether there was significant charge current flowing. For that you would have to compare the initial 'at rest' voltage, then after a minute or so of running you shut it off for a minute and take another voltage reading. If the second reading is higher, you know that some charge flowed into the battery. Then you pull a battery post off and monitor whether the battery voltage drops on its own. You've just tested 3 or 4 systems on the vehicle.
A modern vehicle of course won't like you pulling the battery post off- the computer might decide to 'forget' what it needs to remember in order to keep the optimal settings to run the engine. But other than that, it's quite easy to determine if a battery is at fault or not.
I hate the game- looks like a bad battery, ok, replace it. Well, no that wasn't the problem (but you're already paid for it and won't get your money back) we think it's the computer, replace it. Well that didn't fix it either ($1000 or more later, and it's still broken) you need these new sensors. Later you find that a ground strap wasn't making the best of connection through a layer of paint-
A modern vehicle of course won't like you pulling the battery post off- the computer might decide to 'forget' what it needs to remember in order to keep the optimal settings to run the engine. But other than that, it's quite easy to determine if a battery is at fault or not.
I hate the game- looks like a bad battery, ok, replace it. Well, no that wasn't the problem (but you're already paid for it and won't get your money back) we think it's the computer, replace it. Well that didn't fix it either ($1000 or more later, and it's still broken) you need these new sensors. Later you find that a ground strap wasn't making the best of connection through a layer of paint-
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