That’s interesting cause it was flat this morning when I went to start it and my battery has never been flat so I’m assuming alternator although I could be wrong
You need to work out why the battery is flat…
Best is to take take the earth lead off the battery and measure battery voltage at the posts. Doing such will isolate the battery from the vehicle wiring and any shorts or high parasitic loss which may exist and thus pull the voltage down. Now what’s the voltage?
If it’s 0.10V you have likely a sulphated battery as that’s far too low a voltage. A good battery should be at 12.6V or a bit higher. Once a battery drops below 12.4V it starts to slowly sulphate, below 11.8V the rate of sulphation is much higher. Sulphation isn’t good for any lead acid based battery and @ 0.10v, your battery may be “dead man walking”.
So charge up the battery using a
smart charger until the battery is fully charged. It may take 24 hrs to fully charge the battery or it may not charge at all if the battery voltage is really 0.10 Volts.
If battery voltage is really 0.10V, you may need an old style
dumb charger to get it up to 3V before you disconnect the dumb charger and reconnect a smart charger to continue until fully charged. It‘s best not to leave dumb chargers connected to sealed batteries for extended periods as they can boil the electrolyte within sealed battery which will build pressure and vent. Now what’s the voltage when fully charged? It should be 12.6V or a little more. If you are @ 12.4V that indicates a 50% State of Charge (SOC) and if below 12V you are waisting time trying to recover it…
If it’s 12.4V, I’d connect a multimeter (set to the 10A range) in series with the earth lead and the battery earth post. I’d also include a temporary 5A fuse in series with the multimeter (just to protect the multimeter). Is there any current being drawn? This test will check the vehicle systems for shorts or high parasitic losses ( the problem with smart cars is that it can take up to 30 minutes for the vehicle systems to go to sleep but I don’t think your car has such smarts though not certain how smart or dumb your car is). Normal parasitic loss for a VE/VF is 50 to 80mA but your car isn’t so modern so parasitic loss should be less…
If there is little to no current and the fuse hasn’t blown with the battery fully charged, remove the multimeter and temp inline fuse and reconnect the earth lead to the battery post. Then measure the voltage as you start the car. I find an old analogue multimeter best for this test. What does the batter voltage drop to as the engine is cranking? it shouldn’t drop below 10V really though some say down to 9V is ok…
Then when the engine has started, what is the battery voltage? it should be 13.something volts or higher.
As the very last test, and with the battery fully charged, drive to supercheap and get a load test done on your battery with the tester set to the correct CCA. Did it pass? If it failed when fully charged, buy a new battery but on,y fit it if the vehicle systems don’t have any shorts or high parasitic loss (as such will kill your new battery)…
If the battery is really at 0.10V, it’s almost certainly sulphating and as such a fully charged battery may be at 12.4V but will quickly drop over the next day or two… The more sulphated the battery the quicker the battery voltage drops. Again if its below 12V when fully charged you are waisting time trying to recover it…
Such basic tests will give you a better idea as to the condition of the battery and the vehicle systems… If you have a short or high parasitic loss within the vehicle wiring as shown when testing current, then that issue needs to be investigated and corrected else you risk killing the (new) battery.
(Many car batteries are 80Ahr which means they can power 0.5A for 160hrs or just over 6 days… a sulphated batter won’t last 1/2 that…)
