Still don’t understand voltage…

icrude · 12-15-2023, 12:56 PM

So I recently bought my TM that came with 2 6 volt 225ah batteries. Who knows how old they are. I had them plugged in for at least a day. I would assume they charged up. We go dry camping and don’t use any power other than a light here and there. The fridge is on propane. The furnace does kick on every now and then at night. When I wake up the voltage is at 11.6. Now my basic question is, should 225ah batteries deplete that much over one night just because of the furnace, lp fridge, and a few lights? I know there is small draws here and there also, but 225ah batteries are pretty big, I could think maybe 75% charged in the morning, but down to 20%? That makes me think the batteries are bad.

Shane826 · 12-15-2023, 01:09 PM

Batteries could be bad. How’s the water level?

Batteries could be good but need to be fully charged. You plugged in the camper to charge the batteries. For how long? Might be worthwhile to pull them and take them to an auto parts store that can load test them and deep charge them.

Are you running LED lights? Incandescent can be little power piggies. And the furnace blower pulls way more power than you’d think.

You could have a perfect storm of not fully charged batteries that are on the downside of their lifespan with low water and using more power than you would think…

icrude · 12-15-2023, 01:59 PM

Thanks for the reply! I had the trailer plugged in via a 110 adapter for at least a day so I thought that would be long enough to charge them up but I didn’t put a volt meter on them. I usually only have one of the overhead lights on for 20-30 minutes at a time, I don’t turn them all on all evening. Only when I absolutely need one. I totally get that the heater could be taking a lot, but I didn’t think enough to drain these bigger batteries. Maybe I should do a proper load test on them.

Shane826 · 12-15-2023, 02:52 PM

Pop the caps and check the water level. If the water is really low you’ll never get much use out of them and it can ruin the batteries.

Also keep in mind you really only have ~105 useable amp hours as you don’t want to run lead a use batteries below 50% as it hurts the battery.

**Bill** · 12-15-2023, 05:40 PM

As Shane said, a first step is to make sure they are fully charged initially. Charge them up using a garage-stye charger or the TM built-in charger. Then disconnect them. Wait at least 30 minutes, and then measure the voltage. The voltage after the delay is their true state of charge.

When a battery is being charged, most of the charging takes place on the surface of the lead plates. It takes a while for the so-called "surface charge" to equalize with the bulk material below it. If you don't wait, you will get an artificially high reading.

https://batteryuniversity.com/articl...surface-charge

Bill

**Larryjb** · 12-16-2023, 11:42 AM

If the batteries are getting old, they may be sulphated. Discharging a battery causes lead sulphate to build up. If it has been discharged too many times, you will have less lead on the electrodes, resulting in less capacity. You may still get it charged up to 12.6 V, but it won't last very long.

Also, what Bill said about waiting 30 minutes. You may even need to wait overnight. I just had trouble with my SUV battery. It started off at 12.4 V (a little weak) after a couple of hours, but still enough to start. Overnight it dropped down to 11.9V and was barely enough to start.

One thing you can try is a desulphater. I have managed to revive a few batteries this way, but if they are too far gone, even a desulphater won't help. (I use one from Powerpulse.) Good luck!

icrude · 12-19-2023, 08:05 PM

Thanks everyone. I plugged it in and it charged and stayed right at 12.7. I unplugged the 110 cord and within 30 minutes it dropped to 12.49. Time to replace the batteries you guys think? It’s two of the 6 volt batteries. I looked inside, not low on fluid. Didn’t think the voltage would drop that fast.

Shane826 · 12-20-2023, 06:46 AM

Leave a light on overnight. One incandescent light. See what the battery looks like in the morning.

**Bill** · 12-20-2023, 07:40 AM

I agree with Shane's quick test. A more elaborate approach is to develop a charge/discharge profile.

Quote:

Originally Posted by icrude

Thanks everyone. I plugged it in and it charged and stayed right at 12.7.

If you measured the voltage when the charger was still plugged in, then you were measuring the voltage of the charger, not the voltage of the battery.

Quote:

I unplugged the 110 cord and within 30 minutes it dropped to 12.49.

This is the dissipation of the surface charge that was mentioned above. Yes, it is expected, and a drop of 2/10 of a volt isn't really very much, and does not indicate a fault.

Quote:

Time to replace the batteries you guys think? I looked inside, not low on fluid.

I don't think you know enough about the situation to make that call yet. Are you able to measure the current being drawn from the battery when the charger is not connected? If so, how much is it?

I would suggest that you first charge the battery, then disconnect the battery from the charger and the TM, and measure the terminal voltage. Wait an hour or more, then measure it again - it will be lower. Then wait a couple more hours, and measure again. Wait 24 hours and do it again. The terminal voltage should be stabilized. Now connect the TM, or a known load, let it run the load for a few hours, disconnect the load, wait for an hour, and measure it again. Now report back the discharge current, and the voltage sequence.

Incidentally, I have never found terminal voltage to be really good indicator of state-of-charge, especially as the battery is being exercised. A better solution is to measure the specific gravity of the fluid with a temperature-compensated hydrometer. They are not particularly expensive, especially compared to the cost of two new batteries. Get one with a glass float - avoid the ones with the floating balls.

But first try Shane's suggestion.

Bill

mickmanor · 12-20-2023, 07:58 PM

While on a camping trip, my tow vehicle battery dropped to 11.6v.
At the campsite, I charged it with my carry along charger, and it appeared to charge.
The battery dropped again the next day, and I made it to Autozone.
Since it was under warranty, and at 11.6v, they replaced the battery quickly.
Well, the battery voltage again was dropping the next day. I made it to a repair garage
that could work me into their day's schedule for a new alternator.

The bill was on the high side, but not out of bounds for the given service.
The warranty is great, although I would need to drive about 500 miles for them to do
any follow-up repairs.

So, my lesson learned is that 11.6v is a done deal.
Good luck!