I would like to understand a bit better the pros and cons of lithium vs lead-acid 12v batteries for a motorcycle, especially during the winter.
Yes, I know, google is your friend, and I have found tons of comparisons posts etc, however the one question I have not been able to find anything on is: how do you balance the lower discharge rate of a lithium battery when the bike is unused, vs the fact that lithium batteries have lower capacities, so things like an alarm or the keyless system might drain the battery more quickly? Which of the two effects prevails, and, therefore, which battery will last longer in the winter if you leave the bike unused for a few weeks (not for a few months)?
I also understand that starting the bike on a cold morning I might have to wait 30 seconds or so, but that's not the end of the world.
In theory, one would calculate the discharge rate of lead-acid batteries (around 4% per week?), then calculate the current draw from alarm, immobiliser, keyless system and whatever else may be on the bike, then estimate how long the battery will last unused.
In practice, my experience is that, in the winter, 12v batteries between 8 and 11Ah go completely flat after a couple of weeks, sometimes even less. Experience of many years with multiple bikes and multiple batteries (they couldn't have all been faulty). That is not explained by the draw of alarm immobiliser etc. I can only suppose it must have to do with what happens to the battery below freezing, so part of the question is if lithium batteries will last longer than lead-acid ones with temperatures close to or below freezing.
I am talking about 12V batteries like this lead-acid one, with a 7.4Ah capacity https://www.yuasa.co.uk/ytz8v.html .
I have an alarm and a keyless system (which I hate but keyless seems to be everywhere now), not a tracker.
A lithium equivalent would be something like this, with a 4.5Ah capacity: https://www.gobatteries.co.uk/product/manufacturers/shido/ytz8v-shido-lithium-motorcycle-battery-lifepo4-ltz8v-gtz8v/
What I care and don't care about
I couldn't care less about saving some weight - I am not racing superbikes in Monza.
My priority would be to have a battery which I don't need to charge with a mains charger every 7 days or so if I don't use the motorcycle in the winter. Winter means temperatures between -5 and zero C (23 - 32 F) at night for a couple of months - so not Miami but not Alaska, either.
I know many people report that they manage to leave bikes with similar batteries unused for a month or so without ever experiencing issues - however, that's not my experience (see above).
Obviously if I had my own garage I'd just connect a trickle charger, but I must leave the bike on the road. I can run a cable from the house, with a cable ramp so people don't trip, but I can do that occasionally, I cannot leave it on 24/7.
Apparently similar but unrelated questions
I have found these other discussions which seem similar, but do not answer my question: