The more orange one (top right) is the latest addition. As you can see, four 100Ah Elecsols fit perfectly in the box (which came with the boat). We started with 3, just in case the 4th didn't fit, so we could put them the other way round, with some supports if necessary. But the three fitted so well and left such an invting gap to be filled, that we always planned to buy another. So when we found that the three were struggling to keep up with the solar panel's output, this was the catalyst for finally buying the fouth one.
The only annoying thing is that the terminals are the other way around, as can be seen from the photo! It just makes the wiring slightly less neat.
And we're noticing the difference already. After an evening of TV/iPlayer watching (cathing up with Dr Who etc), the 'traffic lights' on the regulator still show amber, not red!