Dried Out?
When you charged was the ammeter reading 6 amps constantly for say 12 hours or do you have a proper battery monitor and read 6
ampere hours (Ah) over the charging period? There is an enormous difference in the charge that may have gone in.
Is it that you just cannot see any liquid when looking down the vents? Maybe it was only ½" below.
Did the charger go bad and continually charge over a long period so you know for sure the water has all but gone and you only have concentrated sulphuric acid left?
So how much water did they take?
Have they just been left in a fully discharged state for months as this will do untold damage?
Sorry for so many questions but the likely condition of the batts will depend on the extent of the neglect.
Try a load test.
- After leaving the charger on for 24 hours do a load test.
- Measure the voltage off charge and off load with battery at rest.
- Read ammeter and turn on several cabin lights until you see about ten amps discharge.
- Read voltmeter and note both ammeter and voltmeter readings.
- Leave lights on, but nothing else, for say, 5 hours and read both again.
- If voltmeter reads 12 volts or less then either batteries (and/or charger) probably dead.
- Either - Take batteries to a vehicle battery shop and ask them to recharge and load test. Their tester only takes a few seconds but draws a very heavy current.
- Or - get man who knows how to measure charger output and who has a load tester to visit boat.
- Either of the above should be inexpensive when compared with a new set of house batteries so should be worth a go.