O/T rv battery question-long

My horse trailer has a small living quarters package. When electrical hook ups are available everything runs off that. When a hook up isn"t available, there is a deep cycle, marine/rv battery that will power the interior lights and the water pump. The lq package was put in about 1-1/2 yrs ago.

Most of the time I have used a hook up. When the power switch is on and the trailer hooked to a vehicle, there is a 2 amp draw off the vehicle which is supposed to help keep the rv battery charged.

I"m going on a trail ride this week end and there aren"t any hook ups. Decided it would be a good idea to make sure the rv battery had a full charge.

I didn"t think it would need much, so at first I put my 2 amp trickle charger on. It was on almost 24 hrs. When I checked it yesterday evening, it was still charging which surprised me so I got the big charger and put that on.

The big charger has a digital read out. When I first hooked it up, the display read 13.3. Checked it about 3 hours later and it was reading 13.1. Since its got an automatic shut off, I decided to leave it on overnight and check it in the morning. I also pried open the lids to the battery chambers a little so gasses wouldn"t build up.

This morning when I checked it, it was reading 12.8. I didn"t want to leave it on all day, so I disconnected it.

Now the question, is it normal for deep cycle rv/marine batteries to take a long time to charge up? I"m not familiar with that type of battery so I don"t know how long it takes to charge. I know the battery wasn"t completely down, because the lights and pump still worked well.

Should I switch the charger to the higher 20 amp rate and continue charging? I do want the battery fully charged since there aren"t any electrical hook ups at the place where I will be riding.

I think I'd leave it on the lowest automatic setting and trust it. Leave it hooked up til you leave for the ride. Can you isolate the battery from the LQ? I'd unhook the battery til you need it.

What ever amps come out of it must be put back in.

A medium sized 12 volt deep cycle RV battery is rated 120 amp-hours. That means it can supply 1 amp of current for 120 hours. If dead with a 1 amp charger it will take 120 hours to recharge it. If a 2 amp charger, it will take 60 hours, etc.

12.7 volt is a fully charged battery. 12.5 volts is 80% charged. 12.1 volts is 50% charged. 11.6 volts is dead.

Seems the plates were warming up and the interior resistance of the battery was increasing. So you were applying your battery charger to the chemical solution in series with the plate resistance. So as the interior resistance increased, it subtracted voltage from the battery solution causing the apparent drop. I guess that is due to the reduced number of plates even though they are thicker. I do not fully understand the "physics" of the process.

I have had a similar problem with new and older deep cycle batteries so when charging, to get a full charge, I charge for awhile, let them cool and repeat the process till I feel they are full if using my 10A charger that I use to charge most of my batteries. Or, in the case of my boat batteries, with the built in charger in the boat, I just plug it in and leave it for several days. I charges at a max of 5 amperes and that seems to help them stay cool and charge correctly.

I'm not a battery designer and not familiar with all the new things that have changed since "maintenance free" batteries have arrived on the market. Just telling you what works for me.

HTH,
Mark

My charger has a "deep cycle/marine" setting- I charge up my trolling motor battery on that setting, and it seems to charge up in about the same time period as a normal battery.

I had no idea they were so complicated- glad my charger does the thinking.

There is a switch that must be in the "on" position for the power to draw from the battery. I keep it in the "off" position until I need it.

Theres just too many variables and unknowns to give you any exact answer. How long it takes to charge depends on the initial charge state of the battery,,,,,,,,,,How many amps the charger is pumping through it,,,,,,,,,The temperature,,,,,,,,The charger design (smart or old fashioned DUMB lol Charger)

That being said if you just have garden variety dumb chargers around Id start with the higher amp one like a 20 or 30 ect and let her cook a couple hours or so then put it to a smaller 2 to 5 amp charger and leave it several hours. If she charges to such a point shes outgassing bad and boiling over THATS TOO MUCH. Of course keep the caps off so you can observe whats happening but DO NOT ALLOW ANY SPARKS near the battery especially its top.

If she reads 12.6 volts or a bit more (depends on battery state and temperature) shes pretty good but that plus a hydrometer test should give you a good idea of the state of final charge.

John T

I have had lots of batteries not only in my travel trailers but when we had a 47 foot sail boat that we traveled on. In my experience most alternators charge at 14.4 volts and most chargers charge at close to 13,8 volts. As previously said a battery should be full charged at 12.7-8 volts. If it reads higher than 12.8 volts it is due to the charger inputting 13.8 volts and once disconnected the battery will settle down . A smart charger will shut itself off until battery drops to 12.4-6 volts and then start up again. You should be ok for a few days but if I were you, I would install a send battery with a boat 1-2 both switch. That way you use one battery until its down and still have a freh one for extended stays.. Have fun. as a side note, next time spend the extra for a glass mat battery. They last longer, charge quicker and are superdependable.

I have flatbed that has electric over hydaulic brakes and a hoist and winch which requires an on-board battery. The trailer will set between weeks and months between trips so i have learned to put a small battery maintainer on the battery. This keeps the battery charged and prevents the coating that reduces battery life to a minium.

Sounds good.

battery has been chronically undercharged and at too low a rate at only 2.0amp. A 20amp rate is minimum to limit sulphation.

So why is the market saturated with Schumacher 10 amp chargers and no 20 amp? Got to go to a 50 amp charger to get that and then you have to babysit the battery and clean up the H2SO4 bubble out mess when finished or face a possible explosion of a "sealed" battery. And why are trickle chargers getting real popular? And why do bass boat built in chargers limit the rating to 5 amperes per battery knowing full well that most of the batteries are either dual purpose or deep cycle? And why do some chargers have a "Deep Cycle" charging rate?

Besides what is sulphate up?

How much current does the alternator shove into the battery as it sits in that high heat under hood environment? How much bubbling and boiling over? Sulphate up is the opposite of sulphate down.

You have a point; sort of. Your (ones) alternator, mine for example in my OTR vehicle is 100A rated but rarely has to supply that to recharge a normally functioning battery. You and I both know the warnings from battery and alternator mfgrs. that if you have a fully discharged battery to charge it at a slow rate outside the vehicle, don't throw it across the alternator "dry"; but you knew that.

Besides unless you have a discharged battery, the alternator seldom has to put out that much current to recharge starting power and if you are using your boom boom box, it and the battery are supplying power to it simultaneously so the battery is not having to eat all that much VI.....but you knew that!

Apples and oranges.