I bought this torch/flashlight as a quick solution for a failed bicycle headlight in 2020 and I like it a lot because it delivers a similar experience to low-beam car headlights. Unlike many other bike headlights focused to distance, this zoomable torch at the wide end lights up decent part of the road including a bit of its neighbourhood while remaining friendly to drivers in the opposite direction.

The only problem is its terrible contacts that have to be cleaned after every battery recharge. Otherwise the flashlight tends to switch modes, change its intensity or even turn off completely. The original 3xAAA battery holder was completely useless, with this LiOn battery it's at least usable with regular contact scratching.

I believe there are tons of various snake oils available - but is there a stuff that would prevent the contact oxidation for some relevant time (say at least two months)?

Alkaline batteries leaked? Don't buy a brand that are known to leak. As far as I know, Panasonic, Energizer and Duracell here in Israel, are known to leak at EOL.
Toshiba alkaline batteries don't leaks and have very long life.

No no. There was no battery leakage.
It's just the cheap material (and maybe also not very clever shape) of the contacts.

The battery used is rechargeable LiOn battery (Firefly brand).

Buy Maglite.

Maybe try opening it up and put a dab of solder on the contact? You could also try sanding it first.

Maybe try opening it up and put a dab of solder on the contact? You could also try sanding it first.

Thanks, that sounds like an interesting idea. Not sure with the spring, but at least the cap contact is worth trying.

Make sure that there somehow is enough contact pressure.
Apply some vaseline to the contacts to prevent oxidation.

I've given up on trying to find non-leaky alkaline batteries tbh. No matter whether they are made in USA, made in china, made in belgium or made in germany, sooner or later i'll find one leaking. I maintain the battery stock at work, so i have a lot of batteries (both new and used) going through my hands.
German ones seem the least bad though.

Zinc carbon, of all things, appears to leak the least often.

Wait, you said it uses Li-ion batteries, so how do they leak?

Wait, you said it uses Li-ion batteries, so how do they leak?

I never said that, read my post #2.

Make sure that there somehow is enough contact pressure.
Apply some vaseline to the contacts to prevent oxidation.

As for the pressure - it's better that with the original 3xAAA holder because this LiOn cell is a bit longer but it's still limited by the spring.
I was considering the graphite vaseline earlier but haven't applied it yet in the fear it might make the situation even worse.

No, don't put anything conductive in there. It can spread to parts where you really don't want it to be.