Specific gravity readings from each cell will show the different levels of charge across all the cells.
What your looking for, are ones that are different, from the average of the rest.
The float should be at about the same level for all cells, bad cells will float lower, if at all.
One low cell, will render that battery duff, and will need to be removed/replaced.
Good news a Hydrometer is cheap!,<£10 from a good motorfactor.
Bod
Ps. This won't find your high use items, but will check your battery health!
Putting good charge, into duff batteries, = time & money wasted.
Pss. This is how I found my batteries were u/s. Smartgauge was showing 100%, but would drop quickly, one cell was shorted internally, and sucking charge from the others.
1 cell floated very low, others were fine.