Short answer is: some are, some are not, but batteries and repair are covered under warranty in both cases.
For our high-current draw front lights we chose to optimize for performance, so we use a specific battery design that guarantees high quality cells are used and low-resistance connections to reduce efficiency loss. If we were to design around individual replaceable cells for high power demands, they would have to be larger, heavier, lower efficiency, and have more potential points of failure. Considering the Li-Ion cells we use are rated to maintain 80% charge capacity after 1,000 cycles (meaning you'd have to run your light completely dead once a day for 3 years to see a 20% loss of runtime on average), we'd much rather optimize the design for use during that time, rather than to make the one-time service easier down the road.
So does that mean you'll have to pay us ungodly sums of money in a few years to replace the battery if you're getting 40% less runtime than when you first bought them?
No.
We are proponents of the Right to Repair and have no intention of making our money off service to keep the lights running for years. Basically what that means for you is that we won't charge you for any service or repair that you can only get from us. Since you have to come back to us to get a battery for a specific product, that means we'll cover the cost, including shipping.
For our Blade tail light: the current draw is much lower, so for this application we used specially-designed Copper-Beryllium spring contacts to allow for a standard 18650 Li-ion cell to be used without soldering or special connectors. That means it is user-serviceable by removing 5 screws and taking off the back shell, so if you ever have a battery issue, you can replace it yourself instead of sending in for repair.
Note that using a standard cell means any random battery could be installed, which could certainly change runtimes and performance, so we recommend contacting us if you have any questions or issues with batteries so we can ensure peak performance long-term.