combining battery groups a no no?

[Lumatic]

My 93 Excella has 2 group 27 batteries in enclosed battery cases. How would adding a second pair of group 24s or for that matter group 31s work out?

[Drathaar]

It all depends on how they are electrically connected. It can be done, but needs to be done correctly. If you're putting them all in parallel, they should all be of the same size and age. If there will be two sets that you switch between, they could be of differing sizes between the two sets, put each pair should be of similar age and size.

Personally, I wouldn't do it. I'd think about four 6VDC deep cycle batteries in series parallel if you're just looking for lots of capacity. Or, be able to easily recharge the pair of batteries you currently have.

[nvestysly]

I'm no expert but everything I've read/heard indicates this is a bad idea. Apparently the batteries, no matter what type (flooded, AGM, maybe even Li) need to be installed at the same time, must be the same type/rating, etc.

So, if you believe the experts your idea won't work. It may work for some period of time but it will likely cause problems at some point.

It makes sense to have all the batteries the same. If any one of the batteries is weaker than the others or has some other variation it's not difficult to imagine the system develops a "weak link" and will not work properly.

I am considering a battery upgrade and will likely add up to four new AGM's that can be put inside the trailer under the front couch.

[nvestysly]

Originally Posted by Drathaar

It all depends on how they are electrically connected. It can be done, but needs to be done correctly.

I'm not sure what this means??

If the old batteries are "bank 1" and the new batteries are "bank 2" and they are wired separately, charged separately, discharged separately I guess it could work. If that's the case that sounds like too much work and will not really provide an upgraded battery system in my mind.

[Drathaar]

Originally Posted by nvestysly

I'm not sure what this means??

If the old batteries are "bank 1" and the new batteries are "bank 2" and they are wired separately, charged separately, discharged separately I guess it could work. If that's the case that sounds like too much work and will not really provide an upgraded battery system in my mind.

That is one way of doing it. Two separate parallel pairs.

Another way would be four, all in parallel.

As I mentioned, it isn't something I would do. I can be done, but why?

[AnnArborBob]

Assuming that you want all the batteries in the same bank (i.e., and not in two separate banks - and why would you do this anyway??) they should be of the same brand, size, type (e.g., wet cell, AGM or LiFePo) and vintage.

[Shacksman]

I do it all the time and the world hasn't come to an end yet.

[BoldAdventure]

Do you want to do it half assed, or do you want to do it the correct way? That's the question here.

[Lumatic]

Originally Posted by BoldAdventure

Do you want to do it half assed, or do you want to do it the correct way? That's the question here.

Just want an answer to my question

[BoldAdventure]

Sure, you totally can

Let’s see what our battery guru, Justin at LifeLine Battery says:

“It has previously been said that this is not a good idea; however, we have done some pretty extensive lab testing and we can find no differences in the batteries. Age is important but size is not. You can safely mix and match battery sizes in one bank.
Also, Sabre Yachts does this from the factory. This was one of the reasons we started testing this scenario. Sabre use a GPL-4DL and when they want to upgrade a battery bank they add a GPL-31T.”

Source

[nvestysly]

Originally Posted by BoldAdventure

Sure, you totally can

Let’s see what our battery guru, Justin at LifeLine Battery says:

“It has previously been said that this is not a good idea; however, we have done some pretty extensive lab testing and we can find no differences in the batteries. Age is important but size is not. You can safely mix and match battery sizes in one bank.
Also, Sabre Yachts does this from the factory. This was one of the reasons we started testing this scenario. Sabre use a GPL-4DL and when they want to upgrade a battery bank they add a GPL-31T.”

Source

That's useful information and substantiates another post above.

However, I think there may still be caveats to this scenario. For instance, I suspect it's not good to mix battery types such as AGM and flooded.

As Justin says, mixing new batteries and old batteries, regardless of type, is not a good combination. That may be part of what the OP is asking.

[OTRA15]

If affordable uniformity is the top shelf solution and best investment for the long haul IMO. Pay upfront now to minimize unexpected costs later.

Simple

[Shacksman]

My half assed solution is 2 group 24 hooked to 1 gr. 27 hooked to 1 gr 30. Lots of power and in 17 years only 3 batteries replaced.

[Lumatic]

Originally Posted by nvestysly

As Justin says, mixing new batteries and old batteries, regardless of type, is not a good combination. That may be part of what the OP is asking.

My mix and match question is based on my layout. My classic has 2 battery compartments each of which will fit one series 27 battery in the front of the trailer. I am changing out the front couch which gives me access to this area. I may be able to fit 2 additional series 24 batteries in the front of the trailer but probably not series 27. There is also a metal box in the A frame which may hold a battery or 2. . If I add batteries under the couch I will need to use AGMs or make additional vented battery boxes. I could also lay AGMs on their side.Not adding batteries now, but maybe down the road

[nvestysly]

Originally Posted by Shacksman

My half assed solution is 2 group 24 hooked to 1 gr. 27 hooked to 1 gr 30. Lots of power and in 17 years only 3 batteries replaced.

Shacksman,

Even though BoldAdventure referred to the mixing approach as half a$$ed he went on to provide information from LifeLine that indicates mixing sizes of batteries does not seem to create a problem.

Is there a particular reason you take this approach? Space is a limitation in most trailers so it's useful to select battery sizes based on where they fit.

Are you using flooded, AGM or something else?

Do you ever mix battery types? What about mixing brands?

I know you have lots of experience with trailers. When you say you've only replaced 3 batteries in 17 years - was that a set of 3? or, 1 battery in 3 different trailers. I'm curious how your approach works with old and new batteries or if that scenario has created problems.

Thanks

[Shacksman]

I mix them because that's what I have. All flooded batteries and different ages and brands. I never worried about them as they really don't cost that much when compared to all the other stuff you need repaired.
I keep 3 in the back of the truck with solar on the truck cap to keep them charged and a heavy #4 wire to hook to the trailer big battery when close to it. All seems to work fine as we boondock in the winter in Florida and have lots of power available.

[BoldAdventure]

I called that because Lewster on here previously has stated that you want batteries of similar capacities for charging/discharging and keeping track of amp hours. I can't find the original post, but it's in this section.

Mixing group 27 and 24 lead acid probably isn't the problem. But mixing AGM and Lead Acid would be a problem since they both require different charging parms. Hence calling it what I did.

But I'm not trying to upsell you. So you could just mix them and blast them. Sure.

[AnnArborBob]

I wish Lewster would chime in here.

I'm not convinced that mixing batteries of different sizes won't result in some charging issues. Sure it might work, in fact we have at least one proponent with some real world experience in mixing battery sizes on this thread, but it seems logical to me that when you try to charge batteries with different profiles together (size, age, manufacturer which is a surrogate for internal structure/composition), some will get fully charged while others might not. So in the aggregate everything may seem to work but in reality you are not getting all the amps you may think you are.

[gecko]

Please don't forget to consider the new weight, too. Anything forward will affect your tongue weight, and anything that is not centered will load up a side or possibly a single tire.

We put in four Lifelines in our 28' 2010 International when new--two in the tongue mounted box (slightly modified for height) and two on the port side forward under the short side of the L gaucho. We've had two tire failures, all on the port side forward (the service side) and I attribute this to the extra 140 lbs on what is most likely our heavier side (wardrobe/oven cooktop/reefer/hot water heater/pots and pans and all kitchen dishes and utensils plus cleaning supplies).

We will be replacing with lithiums this year, taking 280 pounds down to 84, but only removing an effective 55 lbs from the port side since we need the center forward accessible storage and all the electrical devices/connections are on the port side, too.

But It should take about 175 off our overloaded trailer tongue. And we've already upgraded to Sendel 16's and Michelin XPS Ribs.

If I were designing from scratch, no question that I'd out the batter bank as close to the axles as possible. With heavy tongue weight from the factory and our rear bed configuration, that would probably be centered under the foot of the bed (but we would Lise that valuable storage without gaining it elsewhere. But Lewster assures me that with the fuse/circuit breaker panel/charger/inverter/BlueSky and all connections forward, it would be cost prohibited to rebuild that way with the long, heavy expensive wiring required to spam the distance.

[lewster]

My take,

With all of the battery experience that I have and considering what Justin @ Lifeline said in the boat article, I'm not convinced that different sized batteries (assuming all are Lifeline and of the same manufacture date) in a single bank will not draw at differing rates.

I sent Justin a message requesting this info based on his statements in the referenced article. We'll see what he comes back with (if at all).

Until I have empirical evidence of even draw and depth of discharge across all differing batteries in a mixed grouping, I'll continue to use identical batteries in my battery banks.

Remember, you still can't group different chemistries (AGM with gel or flooded cells) as their charging parameters vary widely.

The jury is still out!!!!!!


Lew Farber
RVIA/RVDA Nationally Certified Master Tech
ABYC Certified Master Marine Electrician
Master Tech Energy Systems, Inc.
AM Solar Certified Installation Center*AMS Lithium Batteries
Lifeline AGM Batteries**Magnum Inverters
541-490-6357