Mixing Batteries

[Len]

I have always been told that one should not mix battery types in a bank (gel, agm,acid). I have two banks ( 2- 4d gels and 2-U1 gels.) These fit snugly in the space below by starboard berth. The U1 's are not very powerful - can't turn over the engine even though they are the designated start battery - as a result I am always starting the engine with all four engaged. I would like to change this. My only requirements are that the battery (2) fit into the same space as the old U1's, and that they be strong enough to turn over the engine. Lead acid and gel cell in the U1 size do not seem to work However Odyssey AGM that are almost the same size. have a CCA of 550 each . But than we bumnp into the dont mix and match rule. My Xantrex battery monitor says don't. But I fail to see that it makes a big difference when reviewing the monitors specs. Something must be lurking below view. The technical specs dont specifically state how the two batteries are treated differently (or when they do it is by a small seemingly insignificant difference).
Any techno wizards have a laymens explanation. I'd love to hear it.
Len

[Maine_Buzzard]

Not a wizard- but here's my story.

The different batteries have different voltages when fully charged. If you have a flooded cell connected to an AGM, the AGM is constantly overcharged if the alternator is set to the flooded voltage, or the flooded gets undercharged if you bump the voltage down for the AGM.

They also like to charge at different rates, so connecting an AC charger is a different beast for the AGMs.

Going all AGMs would not be a big mistake. the cost of the charger is a fraction of new batteries, so the upgrade is more a decision of how much to spend?

[Maine Sail]

I have always been told that one should not mix battery types in a bank (gel, agm,acid). I have two banks ( 2- 4d gels and 2-U1 gels.) These fit snugly in the space below by starboard berth. The U1 's are not very powerful - can't turn over the engine even though they are the designated start battery - as a result I am always starting the engine with all four engaged. I would like to change this. My only requirements are that the battery (2) fit into the same space as the old U1's, and that they be strong enough to turn over the engine. Lead acid and gel cell in the U1 size do not seem to work However Odyssey AGM that are almost the same size. have a CCA of 550 each . But than we bumnp into the dont mix and match rule. My Xantrex battery monitor says don't. But I fail to see that it makes a big difference when reviewing the monitors specs. Something must be lurking below view. The technical specs dont specifically state how the two batteries are treated differently (or when they do it is by a small seemingly insignificant difference).
Any techno wizards have a laymens explanation. I'd love to hear it.
Len

There are many reasons for keeping your batteries all the same type.

#1 They accept charge very differently and acceptance rates can not only vary by battery type, wet, GEL or AGM but also by age so even mixing older batteries with newer batteries is not a good idea.

#2 Charging voltages and "full charge" voltages vary from manufacturer to manufacturer. If you have GEL and AGM or Wets the AGM's and wet cell batts would be chronically "under charged" when mixed with a GEL charging voltage of 14.1V.

#3 It's not just Xantrex that says don't mix. The battery manufacturers also say don't mix types. They also suggest not mixing batteries of unlike size, model, date codes or ages.



You "can" mix types with a Balmar Duo Charger or Xantrex Echo charger BUT they should not be in the same parallel or series/parallel bank. If you had a GEL house and an Odyssey starting battery a Duo Charger or Echo Charger could be utilized to charge the starting bank, though not very well. Due to the differing charging voltages between GEL and AGM you'd still chronically undercharge the AGM because the GEL should not be seeing more than 14.1V and the Duo or Echo Chargers are "voltage followers". While they would technically be "isolated by type" they would still be fed too low a voltage for sufficient charging and would suffer from short life..

You are talking about VERY expensive batteries so it will not be a good idea to mix them.. A U1 battery is ideally intended to start a scooter not a marine diesel. While the Odyssey may do it it will be on the "weak" side of capable.... I suspect a single group 24 or 27 will fit where two U1's will unless you have some height restraints. Otherwise you may be best to find a suitable location for a battery bank capable of starting the motor..

[Len]

Maine Sail,

As they say -I agree but.

My choices are limited- The 2 4ds are fairly new so I am not going to replace them yet. The space prevents me from using anything but U1 size batteries for bank 2. However, Xantrex does allow me to designate the battery "type" for each bank as well as the ah size and charging volts. So theoretically I can have two banks with different specs. Possible yes. But, Xantrex frowns on the practice.

As they say- just because it's possible doesn't mean you should do it !

So back to my initial question? If I can designate different charging limits for each bank , what difference does type of battery make?? (They even let you have one 24 volt and one 12 volt baqnk)Or Am I just being stubborn?

Len