Adrian , SLA's are durable and robust (thats my opinion) and dont need looking after much . I am in the fortunate position of having a good supply of second hand batterys from various sources ,mobility shops etc, all i do woth mine is rig a wiring harness up and connect about 6 or 8 of them up together and put them on the charger and forget them .The reason for so many is that the charge on each batt is minimal ,less than 200ma and as they are 7ah batts in question this charge is less than 10% of the capacity, as for the voltage of left batts , as long as there is a show of nearly the output than they should be ok , i have recovered batts showing less than 10v and they are still working , happy charging

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daz