I would guess that 8.5a * 120v = 1020watts is the surge/max since my full-size US refrigerators run at 250w. But I agree with
@floydR - you should be able to pin this down by searching out specs.,
A 'high frequency' inverter will be cheaper (and lighter) - but they don't have any surge capability and typically don't do 100% of advertised wattage so you would get something 2x or even 3x the size you need. An example of an OK/cheaper inverter is this Reliable 24v@2000w -
https://www.amazon.com/WZRELB-Relia...uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl
A 'low frequency' inverter (has a heavy transformer) will be more expensive but they can handle surge very well. Here's an example of a middle-higher-end/more-expensive AIMS 2000w @ 24v -
https://theinverterstore.com/product/2000-watt-pure-sine-inverter-charger-3/ This AIMS can also charge (using grid power) to keep your battery charged.
If you doing this more as a UPS you could even just go with a refurbished APC 1500 UPS such as this -
https://www.ebay.com/itm/APC-Smart-...536180?hash=item3fe67794b4:g:Yr8AAOSwyoNf2lta I have several of these with 7s7p 18650 batteries - the point being that 7s works pretty well with these. A 7s10p can be crammed inside - but the battery doesn't strictly need to be inside so you could do a larger one in the future.
FYI - I'm not pushing either of these brands, they're just ones that I've used personally and have experience with