House Battery Question

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taoshum

taoshum

Well-known member
Joined
May 21, 2009
Posts
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Location
El Prado, NM
Quick summary:  after we returned from a trip, I neglected to plug in the shore power, a senior moment I guess...  Anyway, after a few days my DW returned to the RV to store some clean towels and stuff and then informed me that the lights in the RV were not working.  Actually nothing worked.  So then I noticed that the the shore power problem.  I plugged into shore power and then we had AC of course but no DC, the display in the power panel was dead so I could not even tell if the charging system was even trying to charge.  I checked all the fuses and breakers and found no problems. I measured the voltage on the house batteries (4 GC2 batteries wired to provide two parallel 12V batteries) and found about 1.9 VDC left.  So, I just left it for a few hours thinking I probably ruined the house batteries.

The next day I went back and all systems were working now that shore power was available.  The batteries showed normal voltage.  So, maybe the batteries did survive????  What should I do now?  Do a load test to see if the batteries work?  Are they really charged? 

I did a search for this question but didn't find an exact hit.  Many postings mentioned that these really deep discharges will reduce the battery life or worse.  These batteries are wet cell GC2's and they are about 3-4 years old.  To my knowledge this is the only time they have been discharged this deeply.

G
 
Yep, a load test would give you a piece of mind. Do you normally use Parks with electric, or do you boondock a bit?
 
I doubt there is any way to make a reasonable guess on quantifying the damage that was done, so my advice is to wait and see if they will still function well enough for your use.  Load testing will help tell you the current state, though unless you have recent test results it will not tell you how much of a performance hit you took.
 
You can use a hydrometer to check the batteries. Turn off the disconnect switch and let them set for a while then test. You also need to find out what was left on for them to be run flat like that so quick. My coach can set for weeks unplugged with out running down the batteries.
 
One deep discharge didn't ruin them if they were is decent condition before that. Those GC2 golf car batteries are pretty rugged.  Lead-acid batteries have a limited number of deep discharge cycles, though, and every major discharge like that reduces the amp-hour capacity a little bit. Rarely ever will it simply kill them, though.

From the converter/charger perspective,  badly discharged batteries will look the same as internally shorted batteries and  the charger will either shut off completely or "pulse" the charge until the voltage comes up enough for normal charging to continue. The charger gives it a brief burst and then shuts off to avoid overloading, then it tries again a short while later. Eventually the battery voltage and charge level builds up enough (typically around 9-10v) for the normal bulk-absorption-float charging cycles to operate continuously.

Since those are flooded cell batteries, check the electrolyte level in each cell and top up with distilled water if needed.  After about 24 hours, turn the charger off (or disconnect shore power) and measure the battery voltage with the charger off to see if the batteries reached float charge stage, about 13.6v. If they did, they are very probably fine.
 
What I tell folks is this
Starting batteries.. well run down that low stick a recycle sticker on 'em they are DONE.

MARINE/deep cycle.... Well... Good chance of the above but they MIGHT recover

DEEP CYCLE (GC-2 for example) Stand a decent chance of recovery

As Gary (I think) said.... Load test 'em.  Only way to be sure.
 
Over the years my batteries occasionally have run down to a very low voltage. I plugged into power and charged them back up and they seem to work fine. 

However I only use them during the day while on the road for water pump, etc so I don't know how they'd be for boondocking but we don't boondock at all.

So I'd suggest...check the water levels,charge them up and then test with a hydrometer ($10).
 
The proof is in a hydrometer reading. You could have lost some capacity but they may still work for you. You can't get an accurate specific gravity right after adding distilled water. You will need to cycle/charge them a few times before the reading will be accurate.
 
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