Battery Evaluation ideas
 

I recently bought a used bike with a 36v 10AH battery. I suspect the battery is bad. Here is why;

- despite charging, never get more than 3 out of 5 battery statuslights.

- no load bat voltage before ride = 36.9v
. After easy ride = 36.1v
- riding under full power, lose power until I start cracking again

advise appreciated

You didn't mention the type of battery, whether lead-acid, or lithium. If the latter, there are several types. On is about 38V at full charge, while the more common types would be 42V at full charge. Your charger might have its full charge voltage printed on the label.

For sure, if it's a lithium battery built with the 18650 cells, that should be 42V at full charge, Your numbers indicate a weak battery.

Any replacement will work, but getting one that fits the current mount iis the first pronlm.

Yes, it is lithium battery. Yukon trails sells a replacement for $339 ... so my used bike was not such a bargain after all.

my general prejudice is that people sell used ebikes after they find out what a battery will cost, and they need one. I'm sure that's not always the case, but there are an awful lot of poorly made lithium cells being sold

A used ebike battery should be considered as almost worthless.

Now, it is possible that all ten strings are only charging to 3.69V. There are other possible combinations.

HOWEVER - That number is suspiciously accurate for 9 (NINE) strings charging to 4.1V each. One dead cell is Exactly what happens when a lithium battery is left uncharged for an extended period of time, and the single cell powering the BMS system is completely discharged and becomes permanently dead.

It is often possible to replace the single cell, and/or charge it individually and slowly with a single-cell charger, and bring the battery back to life. Careful monitoring is required, and replacement is best safety option.

Next question on replacement pack is attachment mechanism for the replacement pack and whether or not additional connections and/or an internal controller are also involved. 36V 10 amp is a pretty low-range pack.

I do have the Grinspector to actually measure battery output under a load. I'm currently working on making various adapters to fit a bunch of different batteries.

A graphed output of power over time can confirm if a battery is anywhere near what its claimed rating is.

-SP

take look on Amazon and eBay for a replacement 36V 10Ah ebike battery, they are currently in the mid $200s.

Anyone used a service to rebuild? https://ebikemarketplace.com/blogs/news for example, purports to rebuild.