house battery Question

[bobsw]

I have four 4D AGM house battery's. My question is  what voltage should the battery's be allowed to discharge to before you have to start the generator. I have been told that it will hurt the battery's if you drop below 12.2 volts. I have also been told that with deep cycle battries you can go down to 10 volts, that's why you pay extra for deep cycle.  Both of the people seem to know what they were talking about. I'm confused.

[HB of CJ]

You have very nice batteries.  Did you receive any literature with the four 8D AGM's that may indicate what discharge voltage will work with you for maximum battery life?  The advised discharge voltage varies with the battery type and its application, as well you know.  My best guess, for whatever it is worth, would be 12.0 VDC under about an 8 hour discharge rate.  Good luck. 

[TomC]

Direct from Lifeline AGM batteries- 3 stage charger- 14.2-14.4 volts for bulk, 14.2-14.4 volts for acceptance, 13.2-13.3 volts for bulk.
Discharge rate it 100%-12.8 volts, 75%-12.55 volts, 50%- 12.2 volts, 25%-11.75 volts, 0%-10.5 Volts.  For me, I just use 12.0 volts as recharge time.  If you stay above the 12 volt line, you'll get maximum life out of the batteries.  Good Luck, TomC

[HB of CJ]

I meant to sayss 4 when I rote 8.  Sorry.  My excuse is that I'm a lefty. 

[niles500]

Bob - the level to which you discharge your AGM Batts will indeed dictate the life of your Batts - never discharging your batteries below 10-20% will allow that you can likely get a couple thousand cycles off them, constant discharges above 80% can lower the number of cycles to possibly a few hundred - every now and then your going to have a deep discharge, and that should not be catastrophic to your Batt's if you mostly keep to a discharge of less than 50% - HTH

[Jerry Liebler]

Bob,
    Tom and Niles give good advice.  I'll add that recharging promptly and fully after any use will extend the life significantly and keep the energy storage capacity they start with.  In other words avoid leaving them partially discharged for long times.  This especially important when they are below 12.2 volts.  Sitting partially charged for extended times results in permanently lost capacity.
Regards
Jerry 4107 1120

[makemineatwostroke]

Bobsw, i got this website from another board that has some good information about batteries, inverters, chargers and solar and they have a forum like this board FWIW                                        

  www.windsun.com

[Tim Strommen]

I once heard a very good analogy for how to treat batteries (for Lead-acid, but most of the details apply):  Treat your batteries like a pet dog.

To take care of your "dog", do the following:

• Water your dog regularly
• Excersise your dog regulary, but don't run your dog to death
• Make sure you feed it good food, and allow your dog to fully rest before you excersise your dog hard
• Keep your dog warm, don't let it freeze to death
• Give your dog lots of love and attention

How this relates to batteries,

• Water your dog - make sure you keep enough water in your batteries, so that the full surface area of the plates are submerged
• Excersise your dog, but don't run your dog to death - it best to run batteries and recharge them frequently, but not deeply discharge the batteries so hard that they "lay around panting for six hours...",  this can kill the useful-life of batteries
• Make sure you feed it good food, and allow your dog to fully rest before you excersise your dog hard - Make sure you give your batteries the right charge voltage and sufficient charge current - then make sure you have replaced the charge you take from the batteries and let them rest (trickle charge) for a bit before trying to run a heavy load (if you force your batteries to run a sprint after they just had a snack, it might get a "cramp" )
• Keep your dog warm, don't let it freeze to death - batteries need a certain temperature to allow for easy reaction - with lead acid batteries, letting them freeze may cause them to rupture and leak once the water and acid warms.  This can cause a dangeous situation with out-gassing, or eat your chassis
• Give your dog lots of love and attention - it easy to forget about your batteries, every time one turns the key, they take for granted that they will work - unless you spend the time each week/month to check the water, check for leaks, check the terminals and wire for corrosion etc. - this negligence could result in getting stranded

Cheers!

-Tim

[Lin]

This is coming from someone that has no real knowledge of the subject, but most of what I have read says that 50 per cent should be the bottom discharge.  I would guess that once you get below 12 volts, your probably stressing them.  It would seem that you could go along way between charges with 4 4D's on normal RV loads, but if your pulling some heavy stuff through the inverter, you will need to recharge at about 12 volts anyway since the inverter probably will probably begin complain.

[bobsw]

Thanks for all the great information. I checked out the web sites and some of the battery manufactures sites, all were very helpfull. I think battery wise I am better off than I thought.  Thanks again.