Rolls S-550 to replace S-530 batteries

Re: Rolls S-550 to replace S-530 batteries

For failure--OK in parallels or series (would prefer in parallel over series--but you may not have the option if replacing one battery because of a failed cell).

In general, mixing old and new (i.e., 3+ year old plus new) is difficult. They are at different points in their life cycle and it is no uncommon for a "newer" battery to age faster when mixed with older batteries--And you end up just replacing all of them at the same time when the rest of the bank begins to "crash".

So--If the present batteries are relatively young, adding a new parallel string may work OK. Get a DC Current Clamp DMM (this one from Sears is good enough and relatively cheap) so you can monitor the charging current sharing for your strings (and find bad wiring, open/shorted cells, etc.--perhaps once a week under heavy charging/discharging current).

If you have an older bank (many years old and of questionable health), wait until you can replace the whole bank at once (and, in my humble opinion, one string is best, no more than two to three strings to keep maintenance issues/cost of wiring/fusing down).

And monitor the temperature corrected specific gravity of all of your cells (log at least once a month, check a "pilot cell" more often) to make sure all are happy.

-Bill