Since, you purchased AGS 100Ah, so you will have to buy again AGS 100Ah for to be added in parallel otherwise entire configuration will fall out of specs.
At any stage, may it be solar or ups mode, charging rate should not exceed 10 amperes, that?s a different story that later it becomes
slow.
By adding two 100Ah AGS batteries in parallel, you will make the system 200Ah, then your current charging rate of 15 amperes from solar panels will fall under the specs.
Anyway, 15 amperes is a lot of output from solar panel, you should seriously think of adding two more AGS 100Ah batteries in parallel as you truly will be able to harvest the output from solar panels and this will make your battery bank fall under the right settings as per charging rate rule.
If you are sure that your AGS has an amp-hr rating of 100Ah then alternate option maybe UGS 125 PHEONIX as that also has an amp-hr rating of 100, I would buy this as site clearly says that it been made for UPS application.
So if you have understood then let me repeat that since you have already bought an 100Ah battery so you can only add 100Ah battery in parallel with this setup.
