Can I use 200 Ah (100 Ah X 2) battery on my 'APC Smurt UPS 1400 Va' for long time backup?

That means I have to add extra charging circuit on this UPS??? Then it work fine with 100 Ah Batteries.... It battery line is in Series connection that means 12v 18 Ah (Series) 12v 18 Ah = 24v 36Ah..... I want to connect 12v 100Ah (Series) 12v 100Ah = 24 volt 200 Ah..... If I do so then I can use fan, light pc for long time backup as IPS.... But for this I have to add extra battery charging circuit on it...... Is it correct?????? Pls answer to me...