I just installed 2 new interstate 6v. they will not charge over 13 volts. All my 12 volt marine batteries would take a charge up to 13.6-13.8 volts. Is this just because they are new, a different type of charger is needed(Battery tender plus) or the type of battery.
If so, what are the voltages of each battery? you could have a bad battery.
__________________
2000 Cherokee 29BH with 6V batteries, LED lights & 400 watts of solar power, flipped axles and raised. 2007 Tundra 5.7L DC-LB with lots of mods. C-co, 8/158th AVN Maint.
They should charge to 14.4v (during absorbtion) and float at 13.25 or somewhat higher with the charger hooked up. Unplugged and resting they should settle back to about 12.8 or so. Not sure if it's the battery, or the charger or what you mean by "charge to"
If you can do spec gravities what specifically do you mean by 10 points?
Generally, a cell is bad if it is off the average of the bank by more than .05 SG units. so if you one cell is of by .20 then it does not meet that criteria.
Example if the average of all 6 cells in your bank is 1.265 and one of the cell is below 1.215, then it is suspect. Note that this only applies to one cell. The other rule of thumb is of you can't charge a battery bank to 75% or more, then it is probably needing replaced.
Voltmeter Hydrometer
Open Circuit Approximate Average Cell
Voltage State-of-charge Specific Gravity