With batteries connected in parallel, even if they are identical, you cannot assume they will all charge equally,
ie the charging current will equally split between the multiple batteries.
Most standalone Solar Installs have the batteries in series, which guarantees equal charging currents
through all the batteries.
Either way, there is no foolproof method of ensuring that they are all being charged equally.
With lead acid batteries, the only foolproof method of determining the battery charge is to measure
the SG of the battery acid, which cant be easily done electronically.