Trailer Battery - Monitoring Remaining Volts

[mitch5252]

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My little trailer has a "dummy" gauge to monitor battery, fresh, grey, black - 4 lights showing current condition.
Not too accurate in my estimation, but I have no reason to know this. This is it exactly:



So, when doing a lot of boondocking, is there any inexpensive way to monitor the state of the battery more accurately? I was just looking at rv battery monitors - HOLY MOLY - expensive little buggers. More than I want/can spend.

If I run my new Honda generator a couple of hours a day, through the trailer's converter thing, will that keep the battery in a "safe" condition?

Any other suggestions for keeping my new trailer battery in tip-top condition, and not overcharging or undercharging?

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[Liz]

I would say an hour on the genny will charge it up. But I know nothing about your battery so maybe others with a tt will chime in.

[sharon]

The monitors are notorious for not being accurate for the holding tanks, with good reason, but are pretty good for giving you a fairly accurate reading on the battery. Liz is probably right that an hour should charge one battery. What you don't want to do is drain the battery completely. They don't like it and will retaliate with not taking a charge at all.

[Bethers]

I have one battery - and when boondocking for several days would run the genie an hour in the morning and an hour in the evening, minimum. The time you have to be most careful is overnight. If you use your heater (with the fridge and lights) you will run down one battery before morning. That's setting the heater at a low temp to come on as necessary. So, my heater is turned off at night and I use great blankets - but before I get up in the morning, I turn the heat on - and get it nice and toasty knowing that the genie will come on and charge the battery soon. (Talking about when it gets cold out - like when Liz and I were on the Natchez Trace and it got below 32 - brrrr - that night I did turn the heat on for about 15 minutes during the middle of the night cuz I was awake anyway - keeping it from getting as cold inside). During the day if the sun's out - don't ever turn the heat on if I don't have to. Running the fan to give yourself heat uses a lot from the battery. I switched out my most used lights to LED's to use less also. Before that, I used to use a lantern. And when in bed, I use a reading light, so that uses nothing. You want to make sure you don't run the battery down so that it no longer can give the juice necessary for the gas fridge to keep working. And believe me, I've done this. Learned the hard way - when I had to replace a battery from letting it get too drained. And when sleeping, I didn't notice the indicator light getting to the danger zone.

It was my first summer out that I really thought that battery could do miracles. Ha ... But I learned - the hard way. And, remember, if you're going to be driving any distance, your battery will charge when driving - so no need to run the genie at all. It's the more than 1 night stays anywhere - or if you want to use other battery draining things ...

[AlmostThere]

So what would be the cutoff for how low to let the battery go?

[Bethers]

A good article - http://rvroadtrip.us/library/12v_system.php - read the "Battery Lifespan" section. Then scroll way down to read the numbers that equal "State Of Charge".

[WickedLady]

If you want an accurate reading on your battery get a digital multimeter. It will tell you the true voltage in the battery. Just touch the leads to the posts to get a reading.
If you have an 80 amp hour battery you don't want it to drain down below 40 amp hours; 100 amp hour battery...50 amp hours. A fully charged battery runs about 13 volts I think. You want it always above about 10 volts if I remember right.

[JudyJB]

Sheeesh! I think I will be able to handle defrosting the refrigerator, but I read the article about the batteries and that terrifies me. Plus all the stuff I have read here about converters and other electrical stuff I need to worry about.

I appreciate the education I am getting, but this stuff really looks complicated. Do motorhomes come with a 24 hour help line, or is this forum it??? Wow.

[Bethers]

Judy, I don't run a gage on mine - have (in the past) run mine too low. My battery started holding a charge less often, I replaced it. It's not one of the most expensive items (under $100) and I learned my lesson.

If you want to read it - 10 volts would be a battery run to no charge.

State of Charge 12v Battery Volts Per Cell
100% 12.6+ 2.12
90% 12.5 2.08

80% 12.42 2.07
70% 12.32 2.05
60% 12.20 2.03
50% 12.06 2.01
40% 11.9 1.98

30% 11.75 1.96
20% 11.58 1.93
10% 11.31 1.89
0 10.5 1.75

For longest life, batteries should stay in the green. Occasional dips into the red are not harmful, but continual discharges to those levels will shorten battery life. Blue - dont want to go there at all! That's when you'll see things like your fridge not working, etc.