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Solar panel and battery fix required

Hi We have a tiny house on our front yard, lights, loo pump and on solar but have not been working for a couple of months. I think one battery is stuffed but I'm not sure if just replacing that will fix the problem. Panel is 24v converted to 2x12v batteries right or wrong this is what we are working with. I need it repaired really soon before the people living there come back. Must be repaired before this Sunday 5pm but would prefer it not left till the last minute.