Using 100ah battery externally

Hopefully someone with some knowledge about batteries can help me out. I'm looking to grab a 1$v 100ah Lifepo4 battery to use as an extension to the Elite 100 v2. Just for times where I could use a little extra amount of battery. Would connect to the XT60 port. Theoretically how many times would that charge up the 100's internal battery? I see it has a 51v 20ah battery internally. Thats when my knowledge of batteries just runs out.