Deep cycle battery charge times
I know there's alot of variables but (rough estimate) what amount of time should I expect to charge my batteries daily. My setup Honda 2000 75 amp powermax boondocker charger 2 gc2 golf cart bat...
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I think that basically, you don't really have any idea how full your batteries are at this point. The normal way to tell is to check specific gravity in wet cells, or rested open circuit voltage in wet or AGM batteries after letting them rest.
If your wet cells are not getting to their maximum specific gravity, and relatively even between the cells, they are either getting old and tired or need equalizing. Wet cells in good condition will be in the 1.270+ specific gravity range and not vary more than about .005 cell to cell. Most will show a rested voltage of 12.7+ volts. You need to charge them until the specific gravity doesn't increase any more, and if they are still uneven or low (which is highly likely) they will need to be equalized (15.5v for 1-4 hours our until the specific gravity quits increasing done very carefully).
The only way that I know of to accurately tell if AGM batteries are full is by measuring the amps going to them at the end of charge. It will be something in the range of .3 to 2% of the 20 hour battery capacity in amp-hours only applied to amps. 1% would be 1 amp per 100ah of capacity for instance. You just charge until the amps quit dropping and you are assured of being full. In the real world, it is usually best to stop a bit early to allow for variations due to temperature, etc, especially if you don't have a temperature compensated charger. Rested voltage of above 12.8 volts is an indication of full charge, but in reality you can get that voltage and still be considerably undercharged. Our Lifelines will hold 13.1 volts for weeks with no load on them if full, but 12.8v is considered full, for instance.
Chronic undercharging will "walk down" the capacity of the batteries quite quickly. They need to get totally full something like once every 5-10 charge cycles for long life.
Since the charge cycle will be different for every battery bank size and manufacture, and also vary by depth of discharge, any charger that tries to run on a timer is doomed to either over or under charge you batteries almost all the time. Most are setup to undercharge from what I have seen. I know they all say the extra time is in the bulk stage and the timers don't start until absorption, so they are accurate, but this is not true as absorption time also changes with different depth of discharge. Some very high end chargers try to estimate the depth of discharge by measuring the bulk time, which helps, but is still an approximation. The best charging systems simply measure the amps going into the batteries with a shunt to determine when the batteries are fully charged. Very simple, very consistent, and very accurate.
Getting the batteries totally full will take a long time, as the final few % are very slow to complete. If we go to minimum amps on our 440ah bank of Lifelines from 50% down, it takes close to 13 hours with a 100 amp charger. Only about 2 hours are at bulk full output, the rest at absorption, and the drop from 4 amps to ending at 1 amp takes nearly 1/2 the time. It is not a fast process. If we stop at 2 amps and let float finish the charge, which it will do, the time will drop by about 25% to get to float, but it will take about 12+ hours of float to finish the charge. The charge times that have been suggested in earlier posts are highly unlikely to come close to full charge.
Wet cells will charge even slower than the above, based on what we have seen in our old setup.
Based on the above, I would guess the OP is not getting anywhere near full and is running the batteries in the 20-80% state of charge range essentially all the time, as that is the part of the charge that will come back quickly. Many boats do this same thing to minimize generator run time, and just accept that it will shorten the battery life by something like 50%. With the system he has, it may be his only real alternative. I would, however, suggest that he put on a battery monitor so he actually knows his state of charge, voltage and amperage. They aren't very expensive, pretty easy to install, and give you all the information you need to know what is happening without guessing.
If your wet cells are not getting to their maximum specific gravity, and relatively even between the cells, they are either getting old and tired or need equalizing. Wet cells in good condition will be in the 1.270+ specific gravity range and not vary more than about .005 cell to cell. Most will show a rested voltage of 12.7+ volts. You need to charge them until the specific gravity doesn't increase any more, and if they are still uneven or low (which is highly likely) they will need to be equalized (15.5v for 1-4 hours our until the specific gravity quits increasing done very carefully).
The only way that I know of to accurately tell if AGM batteries are full is by measuring the amps going to them at the end of charge. It will be something in the range of .3 to 2% of the 20 hour battery capacity in amp-hours only applied to amps. 1% would be 1 amp per 100ah of capacity for instance. You just charge until the amps quit dropping and you are assured of being full. In the real world, it is usually best to stop a bit early to allow for variations due to temperature, etc, especially if you don't have a temperature compensated charger. Rested voltage of above 12.8 volts is an indication of full charge, but in reality you can get that voltage and still be considerably undercharged. Our Lifelines will hold 13.1 volts for weeks with no load on them if full, but 12.8v is considered full, for instance.
Chronic undercharging will "walk down" the capacity of the batteries quite quickly. They need to get totally full something like once every 5-10 charge cycles for long life.
Since the charge cycle will be different for every battery bank size and manufacture, and also vary by depth of discharge, any charger that tries to run on a timer is doomed to either over or under charge you batteries almost all the time. Most are setup to undercharge from what I have seen. I know they all say the extra time is in the bulk stage and the timers don't start until absorption, so they are accurate, but this is not true as absorption time also changes with different depth of discharge. Some very high end chargers try to estimate the depth of discharge by measuring the bulk time, which helps, but is still an approximation. The best charging systems simply measure the amps going into the batteries with a shunt to determine when the batteries are fully charged. Very simple, very consistent, and very accurate.
Getting the batteries totally full will take a long time, as the final few % are very slow to complete. If we go to minimum amps on our 440ah bank of Lifelines from 50% down, it takes close to 13 hours with a 100 amp charger. Only about 2 hours are at bulk full output, the rest at absorption, and the drop from 4 amps to ending at 1 amp takes nearly 1/2 the time. It is not a fast process. If we stop at 2 amps and let float finish the charge, which it will do, the time will drop by about 25% to get to float, but it will take about 12+ hours of float to finish the charge. The charge times that have been suggested in earlier posts are highly unlikely to come close to full charge.
Wet cells will charge even slower than the above, based on what we have seen in our old setup.
Based on the above, I would guess the OP is not getting anywhere near full and is running the batteries in the 20-80% state of charge range essentially all the time, as that is the part of the charge that will come back quickly. Many boats do this same thing to minimize generator run time, and just accept that it will shorten the battery life by something like 50%. With the system he has, it may be his only real alternative. I would, however, suggest that he put on a battery monitor so he actually knows his state of charge, voltage and amperage. They aren't very expensive, pretty easy to install, and give you all the information you need to know what is happening without guessing.
