More accurate battery charging indicator

I've read about people charging their battery to 75%, 85% etc so how re they accurately determining this? My battery charger just has 3 lights. I guess it would be more accurate reading from the bikes display?

You should never charge you battery to anything but full. Much of what you read is from people that either were misinformed or didn't fully understand what they read themselves.

 

If you want to store your battery for a while, run it down until it's about 50% charged. If you want an accurate measurement, use a voltmeter to see if it's 36v.

You can buy this charger for $295. You could also buy a new battery for about the same price! This charger won't balance your battery cells, it just charges them to the voltage you specify. Somewhere in the operating manual it says you must charge to 100% from time to time to balance the cells (yes I read it a while ago). You will not save $295 unless you are running an e-bike rental business and have a couple of dozen batteries to look after.

 

Maybe it would be more correct to say "to when the BMS says the battery is full"?

 

We know that Tesla for example is charging 18650 cells to less than 4.2v to make them last much longer. This is the kind of information which makes people think they can charge their bike battery to less to make it last longer too. You can't do that at home unless your BMS and charger is designed to balance at a lower voltage.

 

Storage voltage out of the factory for most Lithium cells is 3.85v.

Dont' worry to much about charging to a specific voltage.

If you use you bike daily/weekly charge it till full, if you are an infrequent user monthly or longer charge to storage charge of about 37 - 38.5v and then charge the night before use. As always get a cheap meter to check when to stop the charge.