Check out this post, and the chart about the battery voltage, and it's relation to being full or discharged.. It has a lot of great information.
Golden_HVAC wrote:RoyB wrote:
Consider this handy STATE OF CHARGE chart...
Also consider this report from Progressive Dynamics on how long it takes to charge a deep cycle battery.
"Progressive Dynamics ran this test on the amount of time it took a PD9155 (55-amp) converter/charger set to three different output voltages to recharge a 125 AH (Amp Hour) battery after it was fully discharged to 10.5-volts.
14.4-VOLTS (Boost Mode) – Returned the battery to 90% of full charge in approximately 3-hours. The battery reached full charge in approximately 11 hours.
13.6-VOLTS (Normal Mode) – Required 40-hours to return the battery to 90% of full charge and 78-hours to reach full charge.
13.2-VOLTS (Storage Mode) – Required 60-hours to return the battery to 90% of full charge and 100-hours to reach full charge."
This is battery charging science - not many ways to get around it...
When camping off the power grid you want to watch your battery voltage and when it gets down to around 12.0VDC (approximately 50% SOC) then you want to do a smart mode charge starting out with 14.4VDC for two hours and dropping back to 13.6VDC for another hour (three hours total) to get your battery back up to its 90% SOC. Then the battery will perform almost like it would if it had a 100%SOC. You can do around 12-14 cycles of the 50% to 90% SOC rates but will have to perform a full 100%SOC after that to keep from doing damage to your batteries.
When charging with the higher DC Voltage the battery will draw the proper amount of DC current to complete its charge cycle. Then it rest back to 12.6VDC showing you it is at a 100% SOC. Your battery will usually rest at full charge of 12.6-12.7VDC after being charged at 14.4VDC and 13.6VDC for three hours...
Something like this at any rate haha..
Roy Ken
This is a very good chart to indicate what voltage the battery will be at while discharging.
Yes charging at 14.4 volts is acceptable (if you are on a generator and want to minimize generator run time and will not mind the battery getting warm and losing water)
Sometimes I would do a "Equalize charge" - that is charge the battery fully with shore power, then let my 10- 15 amp solar charger fully charge the battery, a bit of overcharge at up to 15 volts. While this can heat up a battery and cause a lot of water loss, I would only do this about every 2-3 months and just after filling the battery with water, and then check it again afterwords. This will break up any sulfur deposits on the battery plates and leave it clean. But doing this more often than 4 times a year can lead to less battery life. Charging a AGM battery above 14.0 volts can shorten it's life a LOT because you can not add water to them.
Fred.
