Are there any good battery options remaining for a 20 year old Thinkpad X40 - Recell? Power bank?

I'm trying to keep my trusty X40 in service, since it's the perfect form factor for document writing and editing, but the replacement battery situation has become worse and worse over the years.

Even the newest ones, OEM or aftermarket, are so old that at best they're only lasting half an hour, sometimes an hour for the extended ones, with the typical symptom of a bad/unbalanced cell (sudden power drop about halfway through its measured capacity). Ideally I would need about 3 or 4 hours.

A dicey option is to re-cell one of my packs, either myself or send it to a professional. Unfortunately the cells are hard to find, old, and I might just end up in the same situation as above.

Another is to just use a power bank with a USB-C to DC 15v adapter. It's not ideal having to drag a power bank around, but it's not a deal breaker for me. However, I'm not sure if the X40 will play nice with 15v versus the 16v it's rated for. Definitely not expecting it to be able to charge the battery very fast, or at all, just hoping there's no intelligence that detects the slightly lower plug-in voltage and puts a kibosh on things.

Definitely open to any other options I haven't thought of. It's as efficient as I can make it, with an SSD and the lower power Banias core mainboard. (Not the Ultra Low Voltage Banias, unfortunately, hard to find.) I'd also love to get the extended slice/dock battery to add onto the capacity of my existing batteries, but those are completely impossible to find.

Any advice on how to keep this little guy going will be greatly appreciated!