'Trickle' charging two 6V batteries

[Tom and Sharon]

I have the two 6V batteries out of our trailer while it's stored (too much of a hassle to charge the batteries at the storage location). (The batteries are original equipment Interstates from the trailer production Spring '16.)

I want to get an inexpensive charger to keep the batteries charged while they're at the house -- two questions:

-- Is there any problem in charging the two batteries in series with a 12V charger? (There are 6 & 12 volt chargers, but not as many as 12V only.)

-- Any recommendations for a good charger?

Thanks!

[Brian B-P]

Originally Posted by Tom and Sharon

-- Is there any problem in charging the two batteries in series with a 12V charger? (There are 6 & 12 volt chargers, but not as many as 12V only.)

No, and that would be the easiest thing to do. It will also ensure that exactly the same current goes through both batteries.

Having said that, my guess is that they would be somewhat better off being separately maintained... but I've never done that with mine (they've been connected for their entire working lives). I'm sure someone has a more authoritative opinion.

[War Eagle]

My two cents - since the batteries are already out of your camper, it might be simpler and cheaper to purchase two small single-battery maintainers than a single unit designed to maintain two batteries. Price them out and see what you find in your location. (Battery Tender, BatteryMINDer and Schumacher all get good reviews, and I'm currently using all three brands with good results, including a couple powered by solar panels.)

[War Eagle]

Moultrie also makes relatively inexpensive 6V battery chargers/maintainers for their outdoor products like game cameras and game feeders. Not sure how they would work on deep-cycle automobile-type batteries, but others might have insight into that aspect.

[Tin]

Originally Posted by Tom and Sharon

-- Any recommendations for a good charger?

Thanks!

The only thing I would recommend today is a "smart charger", like NOCO Genius G3500 $60 on amazon or a CTEK . I have a ctek works great.

Deep Cycle Battery Charger: 5 Top Rated Smart Chargers

[alanmalk]

Originally Posted by Tom and Sharon

...
-- Is there any problem in charging the two batteries in series with a 12V charger? (There are 6 & 12 volt chargers, but not as many as 12V only.)
...
Thanks!

Remember, two 6 volt batteries in series IS a 12 volt battery - just in two pieces.

Use and charge them just like one (heavy) 12 volt battery.

--
Alan

[Kountrykamper]

CTEK 7002 is a good charger.

[Tom and Sharon]

I know 2 x 6V = 1 x 12V, but my concern about charging 2 in series would be if somehow they were not equally discharged. Since the charger goes through multiple charging phases, how would that work? In any case, I decided on a charger that does both 6V and 12V.

[padlin]

How could they be not equally discharged?

[Brian B-P]

Originally Posted by Tom and Sharon

I know 2 x 6V = 1 x 12V, but my concern about charging 2 in series would be if somehow they were not equally discharged.

Originally Posted by padlin

How could they be not equally discharged?

It is true that two 6-volt batteries in series can get "out of synch", and have different levels of charge. Ideally this shouldn't happen with the batteries in series (so the same charging and discharging current goes through both), but in practice it happens because batteries are not perfect and internally discharge to a small extent. Any battery self-discharges slowly while in storage without any external connection, and each cell is doing this... at slightly different rates; two groups of cells (that is, two batteries) will self-discharge at different rates and so end up mismatched.

Cells - and batteries - in series get out of synch during charging, not just storage. Not all of the charge put into a battery is successfully stored by the battery, and even "identical" batteries won't perfectly match each other in charging efficiency, so they end up with different charge levels. During normal discharging in use the same sort of thing happens.

This isn't a big deal, and exactly the same thing happens between the cells of a battery (whether 6-volt or 12-volt). When a battery dies, it is often just one cell that has gone bad, but since they are all built into one case the whole battery has to be replaced. With two 6-volt batteries, the usual advice (which makes sense to me) is to treat them as if they were attached to each other: buy them as a set, and replace them together with another set.

So, charging the pair of 6-volt batteries together means just treating them as one big 12-volt battery (as others have already posted), and clearly that works. The question is whether or not there is a meaningful benefit to taking advantage of the opportunity to charge each set of three cells (one 6-volt battery) to the same state of charge and reduce the mismatch.

Originally Posted by Tom and Sharon

Since the charger goes through multiple charging phases, how would that work?

It's the same as with any battery made up of multiple cells: the charger sees the total voltage, responds to that total, and the change between charging modes isn't quite at the ideal point for each individual cell. That's okay - even if there were one charger per cell normal chargers still wouldn't manage the charging ideally.

[alanmalk]

Originally Posted by Brian B-P

...It's the same as with any battery made up of multiple cells...

Exactly. 12v batt = 2 X 6v batts = 6 X 2v batts. (6 holes to add water...)

Now, lithium batteries are another story altogether. But no Escape owners to my knowledge are using lithiums. (I will be first, when they come down in cost to about $200. )

--
Alan

[Brian B-P]

Originally Posted by alanmalk

Now, lithium batteries are another story altogether. But no Escape owners to my knowledge are using lithiums. (I will be first, when they come down in cost to about $200. )

Maybe Elliott will beat you - he seems pretty serious about advanced hardware :

Originally Posted by Defenestrator

I'm thinking about going with a full lithium+solar setup on a 19' Escape that would let me work from the road without hookups and with minimal generator use, as well as being able to run A/C for an hour or two when the dog's left alone.

[SeldomSeen]

We've been using the Battery Tender Plus since we bought the trailer in 2013. I pull the batteries in the winter and leave then on a bench in the garage, connected together with the same jumper that is used on the trailer. The trailer is in a storage lot.

I also use the BT Plus in the summer when the trailer is parked in the driveway. Seems to do the job.

Glenn

[chowlee]

If the two 6V batteries were being used as 6V sources independently, then it would be better to charge them independently. Because they are used in series to provide 12 Volts, they are subjected to the weakest cell of the combined batteries. That being the case, the charging cycle is subjected to that same weakness. So, it really makes no difference because of they way the batteries are being used. If they were used as independent 6V batteries you could reason that charging them separately, you would still have one good 6V battery if one cell failed.

[Tom and Sharon]

Thanks all for the knowledge, wisdom and practical experience -- as usual. As it turns out, I'm getting a charger that can do both 6V and 12V (NOCO Genius G3500), so I might charge them separately when first putting them in storage in hope that as they age, I might have a better chance of noticing a failure of one (unlikely), then leave them in series on maintenance charge while stored.

[JabberwockJazzy]

We took the dual 6V batteries out of our trailer when we put it in storage middle of October and put them in our basement where they have been sitting for two months now. We bought a NOCO Genius G7200 and are wondering if we should connect the batteries in parallel and use the 12V setting to charge them back up and leave them on the Maintenance (trickle) mode for the rest of the winter, or is it better to let them run down more before re-charging? We are wondering if there would be an issue with the battery memory if they don't go right down before re-charging. Maybe that isn't an issue but we're not sure about how that works. Any suggestions or explanations would be greatly appreciated.

[Tom and Sharon]

Originally Posted by JabberwockJazzy

We took the dual 6V batteries out of our trailer when we put it in storage middle of October and put them in our basement where they have been sitting for two months now. We bought a NOCO Genius G7200 and are wondering if we should connect the batteries in parallel and use the 12V setting to charge them back up and leave them on the Maintenance (trickle) mode for the rest of the winter, or is it better to let them run down more before re-charging? We are wondering if there would be an issue with the battery memory if they don't go right down before re-charging. Maybe that isn't an issue but we're not sure about how that works. Any suggestions or explanations would be greatly appreciated.

Note that two 6V batteries in parallel are 6V; 12V if they're in series.

Others who know more will chime in, I'm sure, but as far as I know, there is no memory effect in lead-acid batteries. Charge 'em up with a good charger (which you've got) and leave them on maintenance charge over the winter.

[JabberwockJazzy]

Thanks for the quick reply! Shows you how much I know "in parallel" (lol); I'm pretty sure I meant "in series" so they do act like a 12V battery.

[thoer]

I have been more than satisfied with our BatteryMinder charger. They use a patented high frequency electronic pulses technology rather than high voltages to prevent sulfation. Their explanation made sense to me Avoid Battery Sulfation with a BatteryMINDer Battery Charger so I bought one. They aren't cheap, but by the end of 6 years of use, my dual 6v Interstates were still performing like new when we sold our 17B.

[Ron in BC]

Originally Posted by JabberwockJazzy

or is it better to let them run down more before re-charging? We are wondering if there would be an issue with the battery memory if they don't go right down before re-charging.

Just about anything is better than letting them discharge completely. That was the practice for Ni-Cads of yesteryear. Trickle charge or charge monthly is good, much better than doing nothing or letting them deeply discharge.

Ron