I'll give a somewhat simpler answer than Filligree has. The problem with renewable energy sources is that they are typically both highly variable and not dispatchable (i.e., controllable). The former leads to supply peaks that can exceed transmission capacity or supply lows that require compensating generation elsewhere. The latter means that energy generation can easily be increased or decreased as required, which is of course very helpful for grid management. Dispatchable generation can be increased if supply requires it, or multiple dispatchable generators can be 'redispatched' to relieve congestion in a part of the power grid (by rebalancing generation). Power from renewable sources can be decreased through curtailment, but that wastes the generated energy.

> Is a grid built on renewables and batteries somehow more resilient?

So this is a complicated subject in itself, and a full answer won't fit inside this textbox. Some bullet points:

- Grid stability is maintained by batteries, but not literally. The "batteries" in question are typically rotating generators, i.e. turbines, wind, literally anything where you have an electrical coupling to a lot of physical inertia. That's what keeps the grid running second-to-second; while a power plant might pretend it's outputting a constant 4MW, it actually shifts noticeably from moment to moment. The kinetic energy of the generator helps balance that out.

- Going up from the sub-second range, an overload of the generator obviously would cause the shaft to slow down, dropping the frequency and causing brownouts. Brownouts are bad and can damage the grid, so typically breakers will disconnect if it falls below 49Hz; a 2% drop.

- Baseload plants can't cope with this, as they take multiple minutes to spool up. Minimum; for something like a coal power plant, where you have to shove in additional coal and wait for it to catch fire, it's going quite a few minutes. This is what defines 'baseload'.

- Peaker power plants can increase (or decrease) their mechanical power production in a matter of seconds. These days that typically means gas turbines, though hydroelectric power is even better, and nuclear power could be used for peaker plants -- but isn't; most nuclear reactor designs outside of the navy is a baseload design. France does have some load-following designs, and we need more of those.

- Wind turbines can't increase their output, flat out, but they can decrease it (by feathering, or by using brakes). This is good enough, except this would turn them into 'peaker plants' that can't help with peaks. If we had enough wind turbines to cover 100% of the load then we'd technically be fine, but economically speaking that doesn't work; they'd be at less than 10% power most of the time.

- Wind turbines have rotating shafts, but a lot of the time they produce DC power, linked through inverters, which removes that benefit and makes them act like solar panels in effect. However, this is a purely economic issue; they can trivially be upgraded to support grid stability if the pricing scheme will pay for it.

- Solar panels are worse: They have no inertia! There is no rotating shaft there to cover sub-second usage spikes. That's where complaints about 'renewables causing reduction of grid stability' come from, along with issues like domestic solar needing to backfeed power through distribution lines and transformers that aren't necessarily designed for that.

- But batteries can absolutely help. The kinetic energy of a rotating turbine isn't actually that big; it's not that expensive to pair a solar panel with a battery to build a grid-forming system that acts the same way a kinetic power plant would.