Lithium cells bulging - what are the opinions?

Yup. The thing to remember about the Multi is that it has no current measurement device on the DC side (no hall effect, no shunt). It estimates it from the AC values, since it has a current transformer on the input and output, and theoretically the difference between those two, multiplied by some efficiency factor, is the DC side.

That’s why you can’t exactly hit small amounts of current. Also, it controls the charge current into the batteries by adjusting the PWM ratio of the H-bridge switches, and it also fights a bit with the grid voltage: If the grid voltage tends to fluctuate a little, then the battery current also fluctuates a little. That’s fine when you’re charging at 10A or more… but very noticeable when attempting to trickle.

The solar chargers are much better. They have a hall effect sensor (an MPPT cannot live without that) and they know a fair bit better what current they are making.