Battery/Amp Usage Question

Dave1956 · 11-17-2011, 08:13 AM

Folks:

I have two 12 volt Interstate RV batteries (less than a year old) on my coach for the house. I left the coach parked in storage without plugging into the 110 as my wife and I were suppose to take the coach out the next day, which we did not do.

The coach was left in "use" mode, the refer was running on gas, and no lights were left on. Further, the last day I used it I tried starting the genset several times (another story) and never had it running log enough to power up.

Yesterday when I checked the coach the batteries were reading "fair" or on my control panel about 50% depleated. Question: would the various electronic controls running in the background for 5 days, along with my several attempts at trying to start the genset, run the two batteries down that far?

Thanks in advance,

Dave

GaryKD · 11-17-2011, 08:20 AM

Hi Dave1956,
Gut feel says yep. Check the condition of your batts with a hydrometer to see where they are in terms of wear and tear. Charge the batts first, let them stand without the charger and no load for a couple of hours. Then do the hydrometer.

BryanL · 11-17-2011, 09:28 AM

no need for hydrometer - that is an unneeded safety risk.

You have a good enough idea of the condition of your batteries.

The RV has a residual load of about 10 watts or more for the control boards and alarms. A typical 2 battery, 100 - 150 pound battery bank has a usable energy capacity of about a kilowatt hour or two (12 watt hours per pound of battery). 10 watts for 24 hours is almost 250 watt hours. That means that 5 days of runtime will indeed use a significant portion of your battery capacity.

You don't want to let your batteries get below 50% (12.0v as measured after no significant charging or discharging for at least a half hour for 12v systems) and you don't want to let them sit around without a full charge on them. So, when you find them down, charge them properly (this can take 8-12 hours with a smart charger) and make sure you put a maintenance charger that uses a sulfation inhibiting technique on them when they are not in use (not just a trickle or float charger).

Dave1956 · 11-17-2011, 09:55 AM

Bryan:

Great answer thanks alot! I do have a Charge Wizard installed and typically leave the coach plugged in to 110 between trips. This particular time frame was an oversight on my part due to change of plans. I check the water levels about twice a year on all 4 batteries. I did plug the coach in yesterday before leaving as it will be left alone for another 4 days before our T-day trip.

Thanks for explaining how that works. This is a real learning process for me!!

Dave

wa8yxm · 11-17-2011, 11:58 AM

Answer: YES. they could epically the generator start attempts.

Fact: There are basically 3 classes of battery Starting including Marine, Marine/Deep cycle and True Deep cycle.

If your Interstates are Starting/Marine.. You may need new ones.

Marine Deep cycle, You may be ok at 50 percent but may also show some signs of damage. Below 50 percent you may need replacement. ... Well,,, RECHARGE NOW, try to keep 'em in the 75 or fuller range.

DEEP CYCLE.. Again recharge now, 50 percent is recommended minimum for Deep cycle, They should show no signs of damage. You can go a bit lower on rare occasions, (I've gone a lot lower on occasions) and they will recover fairly well.

All this is based on experience and confirmed by research in case you are wondering.

Dave1956 · 11-17-2011, 01:33 PM

They are RV deep cycle less than a year old...I will check them after 5 days of Charge Wizzard! Thanks.

ottffss · 11-17-2011, 02:25 PM

And the mother of all "phantom" loads? The inverter!

Yes, just sitting there seemingly doing nothing - when it (the inverter) is really doing what batteries like least - a slow continuous drain.

You'll probably triple your "just sitting there in use mode" battery life days by just turning that one thing OFF, that is the inverter.

If you have a clamp on amp meter just try it out and be prepared for a dramatic surprise.