Inverters / AIN / Gateways / Grid failures

Apologies if this has been covered - I've had a search and can't find anything specific - I've also asked Givenergy support and have not had a reply.

Last year, I had a standard 3.6kw AC coupled inverter installed onto an existing 12 panel solar array (from 2017) along with 3 x 5.2 batteries and a new 4 panel array.

Without thinking things through, I then went an added a 9.5 battery so I now have just the single inverter controlling the two different panel arrays and 25kwh of battery. Obviously, now / summer, it's not an issue for charging the battery as the solar will do that - but in Autumn / Winter, there's not enough time in the Octopus Intelligent Go cheap rate to fill them.... so, a couple of months ago I thought... "can I just change the inverter to an AIO6" - give me even more battery that I don't really need but it would solve the peak power issue.... and then the grid outage issue in Spain / Portugal hit last week and it made me stop and think some more - I have tons of battery storage and solar and yet if our grid did go down (yeah, yeah, "they" all say it's not going to happen here, but whatever), I may as well not have either - everything is reliant on a grid connection.

So, I look at the Giv-Gateway - and from what I can see, yes, it works with the AIO - but I can't connect any of my other batteries to it..... is this a correct assumption?

So, if I want to be able to fully charge my batteries from the grid in autumn / winter I need to swap the current 3.6 inverter for an AIO (and have additional battery storage) but still not be able to have an off grid capability unless I swap the current inverter for 2 x AIO 6, get a Gateway and sell the current batteries. I think I've got that down right....!

So couple of things to note - your existing 3.6 inverter & batteries are Low Voltage.
The AIO is High voltage.
The batteries are not compatible with each other.

You are that invested in the Lv kit now that I would honestly not look at going AIO as you’ll lose a fortune (& I am one of ‘they’ in that realistically the chances of a blackout is slim & let’s be real, it wasn’t off for weeks) plus you do already have backup capability built in to your existing setup, you might just not know. It’s called an EPS, and there are terminals on the inverter that continue to provide power in a power cut. If you Google Givenergy EPS you’ll find various methods of connecting it which in all honesty I can’t be bothered to regurgitate as it’s BBQ time!

What you can do is just add another Lv inverter to your existing and split your batteries up so there’s some on each one. They’ll charge in the window then. You’ll also get double whatever your current charge and discharge rate is now.
You don’t mention if it’s a Gen 1,2 or 3 inverter already fitted but there may be some benefits to making them all the same Gen for balancing purposes.
There may be cross charging but there’s methods around that.

OK - I'll have a read up on the EPS.... this has got me a little frustrated!