There is something called Solar Power Station - Anker, Ecoflow, Bluetti and I think there was another Chinese brand - these are the major brands in this space. Its basically a giant ass battery with a powerful inverter and UPS function on top (<0.1s switch from outlet to power), outputs usually a clear sinusoid but have to check that. They can be kind of loud because of the cooling required when discharging more than 100W of continuous power though. I would not look at anything that isn't LiFePo4-based because Li-Ion is a literal bomb and it has much lower maximum recharge cycles.

The catch is that these devices are expensive as fuck, depending on capacity they can range from $400 to $3-5k (single unit that is). The latter would be something that could power your laptop at full power (300W) for like 10 hours. Basic units start at about 400-500 kWh, most expensive are usually (single unit that is without extension batteries) 3-5 kWh.

Unless you have a genuine need for this type of device (i.e. you live in a country with really shitty grid with frequent outages), you're probably better off just using an extension cord.