My 1991 Honda motorcycle does this too. I can promise you that it has no smart features. It doesn’t even have a fuel pump. Lead acid batteries just don’t have long shelf lives.

Well I get that lead acid batteries experience self discharge, my 2003 era car will go for over a month with around 20% discharge (it'll be around 12.4V), but after 2 or 3 weeks, my 2020 Honda will be at 50% discharge (around 12.0V).

I'd like to think that at some point the parasitic drain devices will shut down before they drain the battery completely, but I've never tested it beyond that point, I always plug in the charger if the car's going to be parked for more than a couple weeks. I installed a charger plug that comes out the front grill so I can plug it into the battery maintainer without even opening the hood.

> I always plug in the charger if the car's going to be parked for more than a couple weeks.

To this day, since ~1980, I disconnect the +ve battery lead if the cars not going to be used for a few days or parked up in the bush waiting for when we get back from a walk.

Stops parasitic drains and Heisenbug discharges when thermal expansion during a very hot day causes a hard to track short.

My 2019 vehicle's manual explicitly says not to do this, and that if the battery fully discharges you should make a follow-up service appointment to frobnicate the computers. I miss older cars.

I have heard that sudden voltage spikes can set off airbags.

Lead acid gel batteries hold their charge MUCH better than standard lead acid batteries. The difference is gel lead acid often self-discharge around 1% per month but standard lead acid batteries self-discharge on the order of 10% per month. I only use gel batteries on my small engine equipment like snowmobiles, motorcycles, and snowblower.