I don't think you'll find automotive LEDs to be useful in this situation. Nor can you use a chandlier bulb. Sorry.

These new-fangled decorative candles are not at all like the plug-in candles that some of us grew up with. These are electronic gadgets, with control electronics inside the candle. The electronics are probably just barely robust enough to power the low-power LEDs fitted at the factory.

Fitting a random higher power LED (let alone an incandescent lamp) is unlikely to help. At best the candle might work in unexpected ways - flicker too fast or slow, or even quit working entirely as the delicate electronics burns out.

You might be able to fit an LED with greater efficacy (more light per watt of input power). You'd have to choose it carefully, measuring the forward voltage and nominal current used by the present LED, and finding an appropriate replacement from Mouser or one of the other electronics suppliers. The replacement would have to be one with very similar voltage and current specifications, but higher MCd output. Even then, there's no guarantee that it will work right. These gadgets are usually designed as a unit, and changing any component will throw off the balance.

It's kind of like putting an extra 2 cups of flour in your Christmas cookies to make the recipe go farther. Even if they still bake up, they won't taste right.

And even if you could make it work, you might well find that just one upgrade LED costs more - probably MUCH more - than you paid for all four of the candles you have now, even before shipping.

This is the kind of project that an electronics geek might do for the fun of it, but for the average homeowner it's probably not a winning proposition.

I suggest that you give these candles to a friend or a local resale charity, and buy something else that works the way you want it to. Buy them at a local retailer, so you can see how they work before taking them home.