Putting drop-ins and DIY together?

[Aphers]

I've got a 271Ah Lishen 4S pack with a JBD 120A BMS. Working pretty well on my boat, powering the fridge and induction cooker, charged by solar via a 40A MPPT with 520w of panels. The other charging source is a 30A mains charger.

I also happen to have a small drop-in 60Ah from Sterling. I bought this as a bit of an experiment when I was using a trolling motor, and it just isn't getting much use any more. So I was wondering about adding it to my existing system, and if so, how?
The Sterling can charge at 30A and discharge at 60A. It has no communications facility but I can look up the preset BMS parameters and presumably adjust my MPPT settings accordingly.

What will happen if I set up the drop-in in parallel with the larger battery? I'm particularly interested in the ability to draw a larger current.

 

[rmaddy]

This may be helpful:

Search results for query: parallel different capacity

diysolarforum.com

 

[Aphers]

Thanks. So first thing to take away is that I should make sure both batteries are at same SOC- which probably means fully charged in practise.
Another interesting point I saw was that you want each battery/BMS to be able to cope if the other one shuts off. Which is potentially a problem on my scenario of a 60Ah+271Ah system. Especially as the smaller drop-in will likely have quite wide parameters and be less likely to go off line than the DIY pack.
Is this such a big problem? Surely people running big banks don't expect a single 4S pack to be able to handle the whole load?