9Ω internal resistance is way too high so the battery monitor may be correct if it is reporting battery capacity rather than state of charge. It should be 1-2Ω really. 4-5 is a bit iffy.
Internal resistance is caused by lead sulphate crystals building up between the lead plates and causing tiny short circuits between the plates. As this happens there is less usable surface area to hold charge so while the battery may be at 12V and appear full to a charger, its actual charge capacity could be very low. It'll appear to be ok after a charge, but probably won't start the car in the morning. I have a couple of old batteries in the workshop like this so I keep one of them on a trickle charger so I can use it for jump-starting. If I take it off the charger it goes flat overnight on its own.
Smart chargers like the C-Teks have a desulphation stage which pulses AC in to the battery to dislodge the crystals, but they don't break down - they just pile up in the bottom of the battery casing. Eventually enough sludge will build up to touch the bottom of the lead plates and then they cause the same short circuits but on a larger scale, so desulphation can prolong the life of a battery, but not recover a terminal one.
Last edited by MikkiJayne; 31st January 2019 at 09:48 AM.
|