Can you Mix Battery Types?

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oldracerjones

oldracerjones

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Chico, TX
My owners manual for my Entegra Esteem 27U class C says to add a coach battery, add the same type. Does that mean if I have a wet 12 volt I can't add a 12 volt AGM? Does it mean if I have a Battery Brand A do I need to add a Battery Brand A?
 
This is a bad idea, all batteries in a bank should be a matched set, same brand, model and age, ideally from the same lot.  Adding in even 1 new battery to a set of the same model that is a few years old will drag the new one down to near the wear level of the old ones in short order.

p.s. if you want 2 house batteries, consider removing the old one and installing a pair a matched 6V golf cart deep cycle batteries wired in series to get 12V in its place if they will fit.
 
Does that mean if I have a wet 12 volt I can't add a 12 volt AGM?
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You definitely don't want to do that. Among other problems their charging characteristics are different.

Assuming you're talking about the house batteries, rather than the chassis (engine) battery, Ike certainly gave you the ideal answer, but if your existing battery is fairly new, you could add one just like it without killing the life of both to an extreme; brand isn't real important, but capacity and other characteristics are important to match. But if the existing battery is, say, four or five years old you're money ahead, plus better operation, by replacing the one with a pair. And the best option, as Ike indicates, is to get a pair of 6V deep cycle batteries (golf cart is cheaper) wired in series (thus making one large 12V that lasts longer), assuming they'll fit.

In our Library (button near top of page) there are a number of articles about batteries, from adding one to maintaining them, etc.
 
Isaac-1 said:
This is a bad idea, all batteries in a bank should be a matched set, same brand, model and age, ideally from the same lot.  Adding in even 1 new battery to a set of the same model that is a few years old will drag the new one down to near the wear level of the old ones in short order.

p.s. if you want 2 house batteries, consider removing the old one and installing a pair a matched 6V golf cart deep cycle batteries wired in series to get 12V in its place if they will fit.
Click to expand...

This brings up one of the big time arguments.
Mixing battery types.
Mixing wet cells with AGM's not always a good idea.
Mixing A starting battery with a Marine/Deep cycle. both sealed wet. Usually works ok.
Mixing GC-2 with a Marine/Deep cycle. well I have a pair of GC-2 and 3 MARINE/deep cycle and no problems though I agree it is not Ideal.

Mixing 12 volt batteries of different sizes.
my pair of GC-2 make basically a 4D
the other 3 are Group 27-29-31 (one each)

NOW.. Batteries in series: (The pair of GC-2) the quoted text applies 100% and that's where it comes from.

But in parallel..  Like I said AGM mixed with wet not the best plan.  but generally mixing different wet's works.

OH. I said Generally. There are exceptions  I won't go into 'em but check the charging specs. so long as the voltages match. you are good (I know of one 12 volt battery that takes a much higher charging voltage. Never seen one. But I know of it. NOT sold in the USA)
 
I think all of the above is valid advice, depending on your tolerance for being less than optimal.

From an economic point of view you are probably better off adding a new matching battery to the one you currently have if it is less than a couple of years old.  This will shorten the life of the new one, but only a little, perhaps making it so the new and old one will both wear out at about the same time in another 2-3 years if they are properly maintained and only lightly used.  Getting much more than 5 years out of generic 12V deep cycle batteries is fairly rare, though a lot comes down to how they are used and maintained.
 
The rule is Do Not Mix Batteries Types...  UNLESS you know what you are doing.  And if you had to ask the question, you probably don't know enough to do that. 

So, it's not a good idea to mix AGM with flooded cells, but mixing different brands of the same type is no worry at all.  In fact, brand names mean very little with batteries, since most brands are just private labels and the batteries mostly all come from the same 4-5 major factories.  However, it's also a poor idea to mix old and new batteries, so I wouldn't suggest adding a new one if the other is more than about a year old.

Mixing different ages and types can be done successfully if you know enough about batteries to evaluate differences in performance and condition and understand how the differences affects charging and battery life. Most RV owners do not, so it's a matter of luck.
 
Thanks all, this really helps. I've done much more research since my question and have reached the same conclusions. My battery is less than a year old so i think I can get one of the same rating and type without seriously affecting the new one. Then I can change the set when they wear out.
 
At under one year old, I'd agree with you UNLESS the battery has been severely discharged multiple times, e.g. down to less than 30% capacity a half dozen times.  It doesn't take much to do grievous bodily harm to a lead acid battery.
 
Gary RV_Wizard said:
severely discharged multiple times, e.g. down to less than 30% capacity a half dozen times.  It doesn't take much to do grievous bodily harm
Click to expand...

That's not even enough to break in a new deep cycle battery, much less do it any grievous harm.  Neglect (left discharged) would be another story.

Mark B.
Albuquerque, NM


 
Gary RV_Wizard said:
At under one year old, I'd agree with you UNLESS the battery has been severely discharged multiple times, e.g. down to less than 30% capacity a half dozen times.  It doesn't take much to do grievous bodily harm to a lead acid battery.
Click to expand...

I know I have keep it fully charged as the MH is on shore power all the time when at home. Only been on one trip so far, 2 days and had shore power there too. I don't know if the dealer let it run down but I imagine that is probable.
 
That's why the rule of thumb is "don't do it". There are almost always too many unknowns to reliably predict success.  But it's not a pass/fail sort of thing either - the performance of the new battery simply degrades more quickly than it might otherwise. Then you MAY end up complaining that the new battery was crappy when in reality it was the old one that caused the loss of power.  It's a "pay me now or pay me later" situation.
 
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