How often should I charge my (lithium) e-bike battery?

Question

I had a retrofitted e-bike running a Leed e-bike kit for 4 years. After 800 charge cycles the battery was toast. However this system is quite basic with both the battery management & charger.

I have replaced that bike with an e-bike running Shimano STEPS e8000. This has more sophisticated battery management (I believe it doesn't use the bottom 20% or top 20% of the battery to extend life) & a more advanced charger.

However I want to make sure I get as much out of the battery as possible. On most days I ride <10km which hardly uses any of the battery capacity.

The batteries on my old & new bikes are lithium-ion.

I've come across two theories for improving battery longevity:

1. Charge every day - that the depth of the charge effects battery health more than the frequency of the charge. So frequent shallow charges is best for the battery.
2. Charge infrequently when the battery reaches a certain level (say 50%). So lowering the number of charge cycles is best for the battery.

I am really curious to know which of these approaches (or another approach) is the best to extend the life of the battery.

Thank you in advance.

Answer 1

I presume Lithium Batteries.

TL;DNR - Charge them as often as convenient for you, always making sure you have more than enough to the next ride.

Battery chemistry makes a big difference - Older lead acid requirements are complex and there is a lot of mis-information and FUD on the internet, some spread by people who don't know what they are discussing, and some by those that do know and stand to make a profit from it. Why am I mentioning Lead Acid - because much information regarding lead acid is incorrectly used when discussing Lithium technology, just adding to the confusion and confusion means profits selling people things they do not need

Lithium - Lithium actually last best if left partly charged - not flat, not full charged, but the difference is not practically significant. Therefore when deciding if you should charge the battery the question is about what suits you.

Lithiums are very sensitive to over charging and over discharge - so much so, humans cannot be relied on to do the job. The chargers are designed to so that they will not overcharge your battery, and the bicycle so it will not over discharge the battery. Despite what some say, you do not need to disconnect the charger as soon as the battery is charged (although its best to turn the charger off to save power, and disconnect the battery from the charger to stop it going flat), and you can ride the bike till the engine stop working.

Worrying when to charge you battery is like worrying about when to fill up you car with gas because driving with more gas in the tank adds weight and wears out the tires quicker. In theory it matters, in practice, stopping to fill up is inconvenient and running out of gas more so, so you fill up when you need to.