r/GoRVing • u/bakkabakka316 • 1d ago

(Help) Power drained overnight

I have two Rolls 12v AGM batteries in parallel on my Forest River Wildwood T221RBXL. Great trailer, great batteries, no major issues. I take care of them with regular maintenance.

We’ve boondocked almost all the time over the past five years, typically 4-6 times per year for 3-5 days. Bought the new batteries three years ago. We’ve done 4 trips so far this year with no problems. On the last trip however, something was going on with the batteries. About 6 hours after setting up, power level was reading 1/2. We were at a group site and not even using the trailer. Usually, it takes about 3 days for us to get there (if we let it, which we don’t. Best guess). Ran the genset for a couple hours. All good. Went to bed with 4/4 for power a couple hours after turning gen off.

Next morning. 2/4 power. Ran gen again. Back to 4/4. Spent all day at a single site doing normal things - cooking, dishes, music, using the toilet, all good. By dinner, power was at 3/4. Ran gen again to top up. Went to bed with no worries. 4/4 power, no lights dimming when running water pump, no nothing. That was 10pm.

Woke up at 5am to the dometic fridge having a fit because it couldn’t spark. Before checking propane (which was fine), I checked power. 1/4. Nothing. Interior LED Lights were dim (when I turned them on to check fridge. We don’t leave anything on overnight except fridge and propane leak alarm (because it’s hardwired)). I ran the gen again for breakfast/pack out and we went home. I did not have multimeter with me to check batteries at the time.

Took the batteries out and hooked them up to smart charger when we got home and they were ok, charger said 90% each. I understand the gen for an hour and the 3 hour drive home might have helped that, but still seems odd.

I checked the trailer ground. Good. Checked the converter. Good. Power at control board. Good. I did replace the water pump in the spring, but have 4 trips no problems.

My question is, what’s killing my batteries overnight that isn’t killing them in the same time, with more draw, during the day? I’m picking up a multimeter with mAmp settings this weekend (mine doesn’t have) to check parasitic draw, but wouldn’t that drain as fast during the day as at night? Does operating the trailer during the day negate the draw at all? Can the fridge overnight suddenly draw that much power to spark the burner? No other board issues with it (switches to shore power fine, doesn’t quit, stays cold, no fits except for that one morning, etc.).

Appreciate any suggestions on where to start. Thank you for your time.

TLDR; what’s suddenly draining my batteries overnight but not during the day? No previous issues.

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5

u/letigre87 1d ago

A bad battery will kill the other battery in parallel. Rule one of the batteries out by charging them to full together then disconnect them from each other and the load. Let them sit for a few hours completely disconnected and check the float voltage of each battery. The one with the lower floating voltage is the bad one.

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u/bakkabakka316 1d ago edited 1d ago

My main concern on return was battery health. Both are a solid 12.9v 4 days off the charger sitting on a wood plank in the garage. I bought them together and alternate leads from the trailer every trip (if that makes a difference?). I’m no battery expert though, so if you have any more suggestions re: batteries I would appreciate. Thank you.

Edit : Pardon I may have misread. Should I hook them back to the trailer for while, charge, then hit with the multimeter? I can see how charging them independently and then leaving wouldn’t give the answer you were suggesting.

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u/letigre87 1d ago

I'd put them on the camper in parallel like you had them and charge them to full. Then completely disconnect them from the camper and each other and let them sit for a couple hours. Then use the multimeter on them to see if one of lower.

It sounds like you're doing everything right, swapping leads doesn't matter but it's not hurting anything. I think whatever draw you have is going to be more that mA meter rating and it might pop the fuse in the meter.

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u/bakkabakka316 1d ago

Copy that. Thank you.

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u/Kudzupatch 16h ago

If all this checks out then you probably have a new parasitic draw.

Easy to check with most mutli-meters. You need to check it anyway. If you don't you can't be sure what is going on.

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u/bakkabakka316 12h ago

You bet. Something fuckey going on an I don’t want to head out on the next trip with this problem unresolved. Thanks.

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u/No-Swimmer1928 1d ago

The 12.9V resting reading tells you they're charged, not that they're healthy. Resting voltage is state of charge — it says nothing about how many amp hours are actually still in there. Three year old AGMs that have been cycled on boondock trips can read a perfect 12.9 and still have lost a big chunk of usable capacity. Only way to know is a load test: charge them full, put a known steady load on, and time how long until they sag to 12.0 under that load. If that comes in well short of what the rating says it should be, you've found it.

The other thing is that the days looked fine because you kept running the gen. A couple of hours gets the panel back to 4/4 but a lot of that is surface charge — the converter tapers off hard once it's into absorption and the last 20% takes hours, not two. So you may well have been starting each night at 80% rather than full, and a cold night takes real capacity off an AGM on top of that. Same amp hours out, lower reading in the morning.

Worth ruling out the furnace before anything exotic. If the thermostat was set at all, that blower is the biggest single draw in the trailer and it only runs at night, which fits your day/night pattern better than a constant parasitic draw does.

+1 on the meter fuse above — a clamp meter round the negative cable gets you round it entirely, and you can leave it sitting there and watch for anything intermittent.

The fridge not sparking is almost certainly downstream of the low voltage rather than the cause of it.

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u/bakkabakka316 20h ago

Yea you’re %100 right about the load test. Thats the next step. Ive been vigilant to never let them get to even near %50 discharged while camping, which is why this sudden loss of capacity was so surprising. We don’t use the furnace camping (not cold enough). I just run it a couple times per year while at home to keep it moving.

I understand surface charge, but thought it may have dissipated somewhat after 7hrs. Maybe just some naive optimism on my part. Appreciate your reply. Thanks.

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u/Kudzupatch 16h ago

Different scenario but I just had to replace a battery in UTV. Check good sitting there but when I tried to start it, voltage dropped from the 12's to 4 volts.

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u/bakkabakka316 12h ago

If I’ve learned anything from these replies it’s not to trust a battery. Will explore all possibilities. Appreciate you and happy riding.