Battery charge level

[gator67]

When we're dry camping and we charge the batteries with the generator, what's the best way to tell if the batteries are fully charged? Or, to be more anal, can one tell if they are, say, 85% or 90% charged?

[gator67]

When we're dry camping and we charge the batteries with the generator, what's the best way to tell if the batteries are fully charged? Or, to be more anal, can one tell if they are, say, 85% or 90% charged?

[Old Scout]

There is a pretty good table out on the Xantrex website (I think), under documents, that shows the "relationship" between battery voltage and % of capacity. However, the note at the bottom of the table assumes the battery banks have been "at rest" for 3 hours for the data to be accurate. I dont have the tables handy but it strikes me that a 12volt battery bank is in "float stage" or full at about 12.7 volts.
The battery purists among us would say the only sure way to determine charge state is to measure specific gravity(SG of 1.26 is full)--but that is too much information for me.

[Algoma]

We have AGM batteries so measuring SG is not an option. On our boat we had a multistage charge regulator which would tell you the state of charge by indicating when it was in "bulk" or "float". I would monitor the current going into the battery during the "bulk" stage and would often turn off the generator before it reached "float" stage to save wasting fuel. This would mean only recharging to about 90% but getting to 100% was too expensive. A good ammeter is the best option.

[Wayne R]

If you have the Xantrex RS2000 inverter charger, you can set the auto start feature to stop at absorb. This is about 75% charge. I don't know at what point WRV switched from Onan inverters to Xantrex in 05, mine has the Xantrex.

[Cruzer]

If you're looking for a voltage to state of charge chart - try the following link:

http://www.rvtechlibrary.com/battery/bat_volts.htm

[gjstacy]

Cruzer,

Thank you for this very helpful information! We've been having real challenges with our Xantrex Inverter properly charging our batteries, and I have wondered about the damage we could be doing to our batteries. This is invaluable info!!

Ron, can you please add this info to the tech site you are building for us Alpiners? That would be great!