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I thought it was timely to remind people of the danger of overcharging batteries.
Although this may only be relevant to inboard diesel engines or engines that require high starter currents to crank over and therefore lesser relevant to outboard motors.
I use the same batteries in my 4WDs and boats - N70ZZs of about 750 CCAs and they are about 90 Amphour.
Yesterday I had a vehicle battery failure, of the type that many would be familiar with. It is where you have the inkling that your battery is on the way out - the slow not as bright crank - on a diesel engine. Yes just got it started, but the next time really slow and a stall. I turned the key off and on a few times, as you do, and no crank (even bending the key with such force clockwise didn't help! illogical of course why should that improve things).
So I put my fancy smart charger on the battery and left the vehicle for the day, as you would, because it is a Smart charger it will eventually go through all the LED light sequences and when fully charged, switch to Float to protect the battery from overcharging damage.
When I came home the battery was extremely hot, and yes gases were escaping with a strong sulphur acid smell.
Now if that was my boat, the engine hold would have been full of explosive gases (hydrogen and extra oxygen) not to mention corrosive sulphuric acid vapour!
Did the smart (expensive) charger fail? No. It was still trying to get the voltage up on the battery.
So the problem was with the battery. I did not do any test with the battery except to read something like 10.3 Volts across the immediately disconnected battery. I already encountered this before so I knew what happened.
A cell was shorted, so it no longer acted like a 12Volt battery and the Smart charger, and I gather all smart chargers could not analyse this during that part of the charging phase. Later on it can tell you, but the battery was still able to take a large charging current (low internal resistance) so the charger happily continued at full bore. It was massively overcharging the remaining (good) 5 cells!
This is because the dead cell died as a result of it's own design. When I cranked the diesel engine to exhaustion, stalling the starter, the battery was supplying a large current, and the weakest link, a cell gave way. The electric field forces inside the cell made the adjacent plates attract and bend bonding to each other. This short still provided ample current flow because of the ample lead plates. These batteries are heavy duty, and are constructed with plenty of lead, a metal, that conducts electricity very well.
The moral or lesson here is that, do not rely on fancy chargers that can be left on and forgotten. Two, you know when a battery is on the way out; replace it. And Three, don't overcrank (particularly to stall) any engine: it don't crank, battery is "full" but it can't turn, don't continue!
The result as outlined above, at worst could have lead to an explosion including the spraying of dangerous sulphuric acid.
Although this may only be relevant to inboard diesel engines or engines that require high starter currents to crank over and therefore lesser relevant to outboard motors.
I use the same batteries in my 4WDs and boats - N70ZZs of about 750 CCAs and they are about 90 Amphour.
Yesterday I had a vehicle battery failure, of the type that many would be familiar with. It is where you have the inkling that your battery is on the way out - the slow not as bright crank - on a diesel engine. Yes just got it started, but the next time really slow and a stall. I turned the key off and on a few times, as you do, and no crank (even bending the key with such force clockwise didn't help! illogical of course why should that improve things).
So I put my fancy smart charger on the battery and left the vehicle for the day, as you would, because it is a Smart charger it will eventually go through all the LED light sequences and when fully charged, switch to Float to protect the battery from overcharging damage.
When I came home the battery was extremely hot, and yes gases were escaping with a strong sulphur acid smell.
Now if that was my boat, the engine hold would have been full of explosive gases (hydrogen and extra oxygen) not to mention corrosive sulphuric acid vapour!
Did the smart (expensive) charger fail? No. It was still trying to get the voltage up on the battery.
So the problem was with the battery. I did not do any test with the battery except to read something like 10.3 Volts across the immediately disconnected battery. I already encountered this before so I knew what happened.
A cell was shorted, so it no longer acted like a 12Volt battery and the Smart charger, and I gather all smart chargers could not analyse this during that part of the charging phase. Later on it can tell you, but the battery was still able to take a large charging current (low internal resistance) so the charger happily continued at full bore. It was massively overcharging the remaining (good) 5 cells!
This is because the dead cell died as a result of it's own design. When I cranked the diesel engine to exhaustion, stalling the starter, the battery was supplying a large current, and the weakest link, a cell gave way. The electric field forces inside the cell made the adjacent plates attract and bend bonding to each other. This short still provided ample current flow because of the ample lead plates. These batteries are heavy duty, and are constructed with plenty of lead, a metal, that conducts electricity very well.
The moral or lesson here is that, do not rely on fancy chargers that can be left on and forgotten. Two, you know when a battery is on the way out; replace it. And Three, don't overcrank (particularly to stall) any engine: it don't crank, battery is "full" but it can't turn, don't continue!
The result as outlined above, at worst could have lead to an explosion including the spraying of dangerous sulphuric acid.