Dual Batteries - must type be matching ?

 I don't see a problem as long as you don't try to wire them together or charge them in parallel.  That being said, I have had a pair of 12v lead acid batteries that were used separately from one another.  Even though they were only 6 months apart age wise I still did not wire them up together.  Oldest one died last August, the other is still going strong at 11 years.  Replaced the dead one with a Trojan T-1275 golf cart battery. (lead acid)

Originally posted by 77 Sunset Strip *******  And yes- would want to hook them together  ********

Under discharge conditions it's true that AGMs will be a little higher in voltage at the same depth of discharge, meaning that if they are in parallel with a flooded battery the AGMs will be at a lower state of charge during discharge. No good but not the end of the world.

What's worse is that
it's the other way around during charging. You can see that by looking at your solar charge
controller voltage settpoints.

AGMs need bulk and float charge voltage settings that are lower than flooded batteries. And there is no equalization charge setting with AGMs.

That means that if you set your solar charge controller for flooded batteries you will be overcharging the AGMs. That's bad because there is no way to add water to them to make up for electrolyte losses from overcharing.

Worst case AGMs can overheat from excessive overcharging, while flooded batteries don't. Reason is that overcharging converts water to hydrogen and oxygen in the battery. That shows up as the bubbles you see in flooded batteries while being charged. So in flooded batteries the two gasses just disappear into the air, and you have to add water periodically to compensate.

But in AGMs and other "sealed" batteries they are recombined into water within the battery. That is good up to a point as you don't need to replace the hydrogen and oxygen with water. But it's very bad if excessive charging occurs because converting hydrogen and oxygen to water is a combustion reaction, creating lots of heat.

The heat has nowhere to go so AGMs can overheat much more easily that flooded batteries. They can get hot enough to blow battery cases apart. Ask me how I know...

If OTOH you set your solar charge controller for AGMs to avoid all those bad things then you will be undercharging the flooded batteries. That's a safer choice than overcharging the AGMs but you're basically throwing away money on the flooded battery, it won't last long not getting charged properly.

Bottom line is you can't win by mixing the two types, just don't do it. Even the smaller variations from different battery models of the same type or different ages of the same model can cause significant imbalance so avoid that too.

Either just start over or swap your two different batteries into the rpod circuit one at a time like Jato does. If you do the latter be sure to reset your charge controller for the battery type youre running every time you make the swap.