Lipos degrade from the moment their made. I would not buy one to have as a spare just sitting around. I would what till you need a new battery and buy it then.
I am looking for another one to help extend range for long rides. I see riding out to one bar on battery, swapping batteries, and heading back.
When not using it for long rides I would rotate between batteries
I found this online at:
https://rogershobbycenter.com/lipoguide/
If you scroll down to the section titled "Proper Care & Treatment: Storage"....
It talks about a "storage voltage" of 3.8v. I imagine that would be the per cell voltage.
It also states,
"I feel the need to reiterate: the most common problem people have with LiPo batteries is a direct result of improper storage. When a LiPo battery sits for a long period of time (and not at proper storage voltage), it tends to discharge itself. If it drops below 3.0V per cell, the vast majority of LiPo chargers will not charge it."
Again, I think we are speaking of a per cell voltage as I believe most 18650 lithium cells charge to 4.2 Volts maximum. Also it seems to state that if we stored the batteries at the proper voltage they will "not" tend to discharge? Maybe its just at a much slower rate than improper storage voltage....
I thought someone said that after each ride I should fully recharge the battery in preparation for the next ride. I guess that's OK as long as I take that next ride soon and not weeks later. Otherwise, I'm guessing a close to 90% charge is better for storage (3.8/4.2 is about 90.5%) and then charge it that final 10% before the ride?? Assuming a 90% charge equates to the "cells" being at 3.8V... Also, how can we tell when we are at 90% as there's only LEDs on the battery? Being a 48V pack, would that be 43.2V... Ok, I think I'm over thinking this....
Wait, this thread is about finding an alternative battery to the $610 ($550 + $60 s&h) Rad battery and not battery care / use... I'll have to search for that thread.