Purchased my 990 back in June of 2018 ( 2019 model ).
My battery's started having issues as far as holding a charge about a year ago, Got 3 years out of em.
Since I have solar panels on the roof I went with some LiFePO4 battery cells and now have 560ahr's of capacity.
Also installed a 3k Inverter back where my generator is kept and rarely use it anymore.
With the storage capacity I have now using the micro or coffee machine is no problem.
Using the AC for a short period of time works to but not all day.
Hell I can even charge up my E-Mtn bike battery without running the generator.
Cost a bit to do but opens up alot more options as far as using power is concerned.
Good job on those Costco battery's.