Bongo Fury

The battery charger fitted to the Bongo has given up the ghost and I need tp replace it. As it sits behind the sliding door step cover I am limited to the size of the replacement. I have seen this:
https://advancedbatterysupplies.co.uk/p ... -122000hd/
It is almost the same size (slightly smaller) as the one I need to replace.
Question is in the PDF it states that the charger should be disconnected from the battery when unplugged from the mains to avoid battery discharge. As I want it to charge LB and supplement if needed when on hook up would fitting a diode in the charger output lead would this be acceptable solution to the discharge issue?

You really don't want a clever battery charger in these situations because it isn't just charging a battery!
The power pack is actually running all the items directly when its connected and powered, and is float charging the battery at the same time, however the batter charger doesn't know this - it just supplies power in a conditioned fashion.
Your much better off using a standard 12 volt caravan power supply like https://www.ebay.co.uk/itm/Caravan-Main ... 1383274042
These supply a regulated 13.8 voltage to anything connected to the system, this is sufficient to float charge the battery and will supply up to 10 Amps of current for whatever is connected, lights, radio, USB adaptors etc.