question

Very had to give you advise here as we are missing a lot of details

Ie

1. how many times they are cycled,

2. what is the depth of discharge each time

3. are these thick or thin plate batteries

4. are they AGM or Flooded or Gel

5. What Temperature do they operate in

6 if you are topping them up with water is it distilled water.

but as a general guild

all of the above will change how long the batteries last before replacement is needed.

you mention that you never go below 12v well thats over 60% discharge and thus you are cycling the batteries plus you say these are truck starter batteries so they maybe thin plated as well (thus cycling is very bad for them) this is needed for high CCA for Starting current and if this is correct then you are very lucky to even get 4 years out of them.

the voltages that the duo output should be close enough a 0.1 difference is no big deal, and in my opinion not affect the batteries at all

keeping them full will not damage them unless they are getting hot

when charging or using lots of water

Thank you for your quick reply:
Batteries are Varta Promotive Silver 12V 225Ah N9

1. how many times they are cycled,
Not to be determinated... 98% on solar trickle load, maybe max 50 times.

2. what is the depth of discharge each time
regularely mx 12,2V

3. are these thick or thin plate batteries
thin plates I assume

4. are they AGM or Flooded or Gel
Flooded

5. What Temperature do they operate in
+5 to +40C

6 if you are topping them up with water is it distilled water.
not applicable: sealed lead acid
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I have to correct one thing: the starter battery is OK so far but all 3 house batteries are broken.

the voltages that the duo output should be close enough a 0.1 difference is no big deal, and in my opinion not affect the batteries at all

I would agree to this but the difference is in fact 0,4V. Should be 13,4V but trickle charging is 13,8V and the main question is now: How can I adjust the DUO's to deliver 13,4V instead of 13,8V

Thank you

would agree to a difference of 0,1V but the difference is in fact 0,4V. Should be 13,4V but trickle charging of the DUO's is 13,8V and the main question is now:

How can I adjust the DUO's to serve 13,4V instead of the preset 13,8V?