Charging two 6-volts in tandem safety recommendations

I imagine this isn't a new topic, but trying to search brought up too many unrelated results and I got overwhelmed. My 2014 Lance 2295 is equipped with 2 new 6-volt batteries. I had a 160 Watt solar system installed, but I was told by the dealer to remove the batteries while the trailer is in storage and connect them in tandem to a charger so they don't drop below 12 volts (in case there are enough cloudy days in a row to prevent the solar system from keeping them adequately charged). I dutifully went to Harbor Freight and bought a Cen-Tech 60322 2/6 AMP, 6/12 Volt charger. But in reading the instructions and warnings I'm now scared to connect it to my batteries. It says that I need to have minimum 12" battery cable to connect to the free negative terminal (instead of just connecting directly to the terminal) and not to leave the system charging 'unattended'. It has an automatic cutoff when in 12 volt mode so my understanding is that I should be able to leaving it charging until Spring with no worries. I could really use some sound advise here.

Thanks,
Wayniack

My concern would be overcharging, but in the 2 amp mode I?m guessing you?ll be OK.


My suggestion would be to connect the batteries in series then charge them in series in the 12v mode (connect charger to positive of one battery and negative of the other) at 2A, assuming you?re starting with fully charged batteries. Check them in a few days to check for charge and to make sure your charger isn?t boiling them. Also make sure water levels are good. If all?s well, come back in a couple weeks and check again.

The first step would be to throw out that Harbor Freight charger (or return it if you can) and get a battery tender. Then hook it up as previously described.

There are battery chargers and there are battery chargers and there are battery Tender/Maintainers (you need the last tender or maintainer) a good brand is Deltran Battery Tender

Older not smart chargers will over charge a battery, gas it and this gas (Brown's gas) is highly explosive being two parts hydrogen to one oxygen.. Hence the 12" to the electronics requirement.

Smart chargers and Battery tenders.. Will not do this.

And remember two six volt batteries in series are really one BIG 12 volt battery  Treat the pair as such.

With Battery Tenders it is NOT necessary to remove the battery from the RV if you have power to the storage site.. If you do not then

Before removingm battreies take two cans or bottles of paint or nail polish,  Black and Red

Red on all wires hooked to the MOST POSITIVE lead (Ignore the jumper that connects the batteries)

Black on the Most Negative

A couple of wire ties or some tape when you disconnect. If more than one wire is attached to a terminal Tape or Tie the wires together so you do not miss any when re-installing.

The OP first mistake is listening to the dealer. With 160 Watt solar system he should have no need for a battery maintainer. Unless he's parking the camper in a building.

It says that I need to have minimum 12" battery cable to connect to the free negative terminal (instead of just connecting directly to the terminal) and not to leave the system charging 'unattended'. It has an automatic cutoff when in 12 volt mode so my understanding is that I should be able to leaving it charging until Spring with no worries. I could really use some sound advise here.

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That part of the instructions was written by their lawyer to cover their butts from potential lawsuits. The 12" cable moves a potential spark away from a possibly gassing battery and reduces the off-chance of an explosion. And stipulating that it must be "attended" means you can't sue them if the battery is so bad it overheats or runs dry from long term charging. All these things are highly unusual but conceivable.  Given the number of careless or oblivious people in the world, the company has to consider that one of their customers is going to have a bad battery and act without reasonable caution. Thus the CYA.

So, make sure the batteries have electrolyte in them. If not sealed types, check each cell and top of with distilled water if needed.  Then, with the charger powered off, connect the + lead to the positive terminal and the - lead to the negative. Since these are 6v batteries, the two need to be wired together in a series pair to make them into one 12v battery, just as they are in the RV. Then plug in the charger and observe closely for an hour or so, to make sure it is all functioning as expected. Check regularly over the weeks and months to be sure it stays that way. If the battery cases begin to get hot, unplug the charger immediately.

A two amp charger isn't going to overcharge a 200+ AH battery bank even if it runs for months.  And there is nothing wrong with the little HF or similar chargers for this sort of maintenance chore. I leave one on a car we store for several months each year and it does a nice job or compensating for parasitic draw and self-discharge.

The OP first mistake is listening to the dealer. With 160 Watt solar system he should have no need for a battery maintainer

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If the weather is poor enough that he won't be going camping, chances are there won't be much sun either. However, it's only a couple cloudy days now and then, the battery bank isn't going to discharge all that much either. It's a judgment call.

I am not sure but believe this charger may have only 2 modes. 6 volt at 2 amps or 12 volts at 6 amps.

believe this charger may have only 2 modes. 6 volt at 2 amps or 12 volts at 6 amps.

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It's the other way around: 6A @ 6v and 2A @ 12v.  Connecting it to a series-pair of 6v batteries (which forms a single 12v battery), the charger produces a max of 2A, what is commonly called a trickle charge.

Supposedly it goes into an even lower charge mode once the battery reaches full charge. With todays inexpressive electronics, there is little reason to doubt that even in a cheap charger like this.

This comment is a little tangential to the topic, but the explosion possibility is no joke if the batteries are overcharged and not adequately ventilated.  Many years ago I was working in a service station (remember those?) and was charging the 6 volt battery in an old VW bug.  The battery was in a compartment below the floor behind the passenger seat.  After fast charging for two hours at high current I removed the connector without thinking to turn off the charger, and KABOOM.  The spark ignited the hydrogen gas that had accumulated in the confined space and literally blew me back out of the car and onto my ass.  Lesson learned, and well remembered.  Stupid hurts.

Cheers - Joe