As some of you may have seen, I upgraded my trailer this winter, and the new bigger unit came with a pair of 6V Trojan T-105 deep cycle batteries. I am pretty happy about that, because in my last trailer, I managed to run down my single marine battery a few times.

So, just to check things out, I slapped my "smart" 2/10/15A charger on them, and watched. The charger didn't throw any error codes, and slowly ramped up the amperage to 13.6A, which is a hell of a lot higher than my old battery would take. So far so good.

Here's the issue, it'll charge for 24h at that rate, and then throw an error code. This is a feature of the charger. I've restarted the charging now about seven times, so a total of 168 hours of charging at 13.6A. Seems to me, the batteries should be full by now. However, when I go back, every time, the voltage is down to 12.7.

Water levels are decent. The charger is supposed to sense when the plates are sulfated, and it's not throwing that error.

What gives? Are these batteries pooched somehow?

If it matters, this is the charger:
MotoMaster Nautilus Battery Charger,15/10/2A | Canadian Tire

 

What do you expect them to be, and why?

Pop

 

Your batteries are fully charged at 12.7 volts. 13.6 volts is simply the surface charge that dissipates quickly with any small load on the batteries or simply over time. Your batteries will not sustain 13.6 volts, you see that only while charging.

Turn off the charger and turn on a small load like a light to remove the surface charge, and you will see 12.7 - 12.8 volts on your meter very quickly.

Since near all converters in RVs are smart chargers, you probably are not gaining anything by using a separate charger, unless you aren't able to plug in your camper where it sits.

Your batteries are fine.

Steve

 

Heh, maybe I was over-thinking this. Or under-thinking and letting my charger think too much for me. Now that you say it, of course 12.7V is fine as a resting voltage. I probably knew that.

My so-called "smart" charger has a "% full /capacity" readout when connected, and at 12.7, it reads "low".

I guess what got me concerned was that it never got itself to read "full" which it does at some voltage north of 13, I can't recall what it is. These batteries don't seem to get that high, no matter how long I charge it. So, I guess that's my follow-up question, does it matter if the voltage while charging doesn't go as high as I expect it to?

Steve, as for why I'm charging them out of the trailer, it's because it may still get darned cold here, and I like to keep the batteries indoors until springtime to avoid freezing them solid if we do get some cold weather. I have no power available where the trailer is stored.

 

Got the cold part! Didn't read where you were.

As long as you voltage are resting at 12.7-12.8 on new batteries, you have done as much as you can. You also know the charger is doing its job because the batteries are fully charged. Now if the charger reads low and can't bring the batteries up there is a problem somewhere. Otherwise, in my opinion you are good to go. These smart chargers we got aren't always so smart.

Steve

 

Neither am I, so we're kind of stuck between a rock and a hard place here.



Just to make myself feel better, I have the batteries on the charger one more time today. I will look a little later to see what voltage they get up to.

 

Well, it gets up to 14.8V while charging, which the charger interprets as 90% full. Clearly, that's voltage is plenty high enough, and as mentioned, the resting voltage of 12.7V is acceptable.

So, case closed, I was relying far too much on the "smart" charger, and not using my brain.

I learned not to be so lazy, and to actually look closer at the voltages. Hopefully someone else can learn from my folly as well.

 

Well no. It depends on the temperature. Battery charging voltage tables are published for 80F, though as the temperature goes down the charging voltage must be a bit higher than this to overcome internal battery resistance.

 

Couldn't tell but this charger is suppose to be able to charge AGM batteries right?


I pull my battery out of my 5th wheel and put it on the workbench during the winter.


I change mine over to % of charge. It will always read around 40% when I charge it. It about 3 hours it is at 100%.


It does not stay at the 100% rate but for a couple of days.

 

That last 10% takes a while. Batteries "like" to remain in a state of 100% charge and continued charging as well. They spend a lot of time in a semi-discharged state, this sort of evens things up. A battery won't even approach 90% charge till the voltage reaches about 2 (two) volts above the resting open circuit voltage, they start moderate gassing (good) and the electrolyte starts mixing. It is possible to overcharge but it takes real dedication. Batteries are easily one of the most abused components under the hood. Keep them clean, tight shiny grounds and terminals and fully charged, and they will perform. If not, not.

 

I thought about this today and wanted to share one last thought. A few years ago I installed a new converter with smart charging capability, along with a new battery at a dealer's. To make a long story short, the battery went dead and would not charge, but the converter seemed to test fine in terms of voltage. That is bulk, absorption, and float charging stage looked fine, but put an amp meter on it and the charger was only putting out a couple of amps at best regardless of stage.

Didn't think it was possible so I tested with my back up meter on another battery. Same thing. Pulled the converter and install another and all was fine. Sent the converter in under warranty and the manufacturer verified it and sent me a new one. Smart charger was running through the stages too quickly making it a dumb bunny.

Clearly a real rarity as I have never seen it happen like that again.

So, having rethought this issue, if the smart charger is not dropping below 14.4 volts, it is not going to float stage (it should drop back to something over 13) meaning the batteries are not fully charging. Maybe the charger, maybe a bad battery.

I would test the charger on either two six volts in series and test one pair against the other, or do the same with 12-volt batteries to see whether it can correctly stage with either. That way you could rule out the possibility of a bad charger or battery.

Steve

 

I don't know how to use this information to help.

I think the charger is rated for AGM batteries. No matter how long I charge for, it never reads 100% charge, although it has gotten up to 80-90% a few times.

I have had no issues charging other 12V batteries with this charger, the current trailer setup is the 2x 6V batteries in series. This charger can't do a single 6V battery.

So, did we reach consensus that I'm in good shape, or are we still not sure here?

 

I didn't have a very good handle on it till I studied things here:

http://jgdarden.com/batteryfaq/carfaq.htm

Look over the charging tables for a given battery type, as well as the temperature compensation figures. Connect a voltmeter and a charger to a semi-discharged battery and observe how the voltage starts out low and the current starts out high. As the battery approaches a full charge the current tapers off to almost nothing and the voltage rises. For lack of a better term, batteries need to "cook" for quite a while to fully charge. This can be disconcerting and I think the manufacturers leave out voltage displays to avoid returns. Peeps eyes bug out when they see 15 volts on a "12 volt" battery e.g. "There's something wrong with this thing."

Be sure to provide adequate ventilation. Be VERY careful and deliberate whenever working around batteries, the amount of stored energy is considerable.

For most people a charger that will provide 4 to 10 amperes is perfect and this is the recommended range for slowly charging auto start batteries. Different battery types require different charging voltages or they will be undercharged. Small "smart" or float chargers/maintainers won't usually fully charge depleted or sulfated large batteries because they have special protection circuitry to prevent boiling a battery dry. I use a "dumb" charger and monitor voltage and current till thoroughly charged and then hook up the float charger for long term storage.

 

Temperature compensation is available on in the higher-end inverters and from one converter manufacturer I am aware of, as far as I know. On my inverter, I have a temperature sensor that mounts on the battery and I can actually watch the charging modulate with ambient temperature at the controller for my solar panels.

I haven't seen 15 volts, unless the charger has an equalizer setting

Steve

 

Just for my piece of mind, I know your charger stages to 14.4 for the absorption stage. I was just wondering if it then drops back down to about 13.5. For example, if your charger shows 12 volt batteries as 100% charged, why not with the new 6-volt batteries. But maybe it does and this is probably just me obsessing.