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12 Volt RV Battery

The following info posted by Mickey

Lead acid batteries prefer to be charged by a regulated constant voltage source. Depending upon how long you intend to leave the charger on, will determine the proper voltage. A good compromise for a 12V battery is 13.8V. At this level you will never over charge the battery and "boil" it dry. I've only had to add water once in 2 years and I'm on shore power 24/7 11mo's/yr.

I'm not familiar with your model converter but for the very common Magnetek 6300 series converter, there is a separate PCB that controls the charging function and its output voltage is adjustable. The newer Magnetek's are a different design and all of the output is available for charging the battery. These chargers are regulated and are set close to the 13.8V I've mentioned.

I see no need to remove your battery, specially if you leave you rig plugged in during the winter as you've noted. Freezing point for a battery that is fully charged is WAY below zero.

The only thing you should check on is what the voltage level is for the charger section of your converter. Idealy, 13.8V is what you want. If you find it over 14V, long term charging will over charge at this voltage level and will "boil" the battery dry. At 13.5 - 13.8 you may need to add water evry 2 yrs. One last thing, If not plugged into shore power, I wouldn't leave the battery connected. There is alway a few items that will draw the battery down.

Many thanks, Mickey!

Mike adds ...

Batteries should be checked with no load and after they've been at rest for at least three hours.
Here's a general chart showing state of charge to available volts from a 12V battery:

  • 100% 12.70 volts
  • 90% 12.50
  • 80% 12.42
  • 70% 12.32
  • 60% 12.20
  • 50% 12.06
  • 40% 11.90
  • 30% 11.75
  • 20% 11.58
  • 10% 11.31
  • 0% 10.50

Although many people discharge deep cycle batteries below 50%, I don't. It's also important to recharge the batteries as soon after use as possible. IOW, don't leave them discharged while in storage if at all possible.

Al Comments:

Given a simple single stage converter / charger the generally accepted voltage of 13.8 is a compromise between a high enough voltage to provide a reasonal re-charge and not boiling off the bateries. Sophisticated multi-stage chargers will generally have a temperature compesation circuit to adjust the actual voltage. For instance, the "optimal" float voltage for a Flooded cell lead acid battey at 100 degrees F is 12.9 volts and at 30 degrees F is 14.3 volts. Gel Cell and AGM batteries require different voltages. The sophisticated multi-stage chargers will also have setting to select the battery type. Simple single stage converter / chargers do not have this capability. Having had both the "simple" and the "sophisticated" types of charger I can assure you that there is a tremendous difference in battery performance in terms of life, effective AH capacity, etc.



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