Reapr

Hi, I have a small system just to beat load shedding. A little Mercer 1400W (24V) desktop type inverter. I got this 2 years ago with some cheap batteries for 200Ah total - all they had to do was power 2 PC's and a router through load shedding, and they did that with roughly 75% left after each power cut. Well it is now 2 years later and the batteries are done. they barely do 20 mins now, so time for new batteries, but reading here about lithium batteries, leads me to believe they should last longer than the lead acid ones (although at a cost) Problem is, my little Mercer cannot do Lithium, only Lead-acid, but the S100's for example say that they are "drop in" replacements for lead-acid batteries - does that mean they will work ok on my Mercer, how do they do that? Doesn't Lithium batteries voltage work differently as they discharge? Or will the BMS in the battery cut the power? Colour me confuse and your help & advice would be appreciated. Do I go for the Lithiums, or just stick with Lead acid and replace every two years? Thanks! EDIT: Ok, seems no one knows, so I'll just buy some more lead acids