Example of Ebike Battery Disassembly and Diagnosis

My 1 week old reention dorado LG 48V 17Ah battery charges to only 54.2V. That isn't so good, eh? It might be due to a cheap controller inside or cells not up to par? Or the BMS cuts it off early?
 

DouglasB

Active Member
That guy is great. I think he missed his calling. He looks like a young Jim Carrey. Even has that whacky twinkle in his eye.
 

Alex M

Active Member
Seems logical to disconnect BMS if extended storage without charging is planned.
Never thought that BMS could discharge it that bad, I guess not all BMS are created equal. Voltage at the beginning of storage (for this particular customer) is a big unknown, it's possible it was already discharged down to 2V before storage.
 

Thomas Jaszewski

Well-Known Member
Seems logical to disconnect BMS if extended storage without charging is planned.
Never thought that BMS could discharge it that bad, I guess not all BMS are created equal. Voltage at the beginning of storage (for this particular customer) is a big unknown, it's possible it was already discharged down to 2V before storage.
Its really amazing to see how cheap many BMS are used. I have three Luna batteries with $10 retail BMS.
 

Alex M

Active Member
Its really amazing to see how cheap many BMS are used. I have three Luna batteries with $10 retail BMS.
This is a Klondike - for unscrupulous Asian suppliers. Put it in, nobody will know as long as it "works" - meaning the motor is spinning somehow. Isn't BMS supposed to prevent such a catastrophic discharge by opening the contacts and shutting itself down too?
 

Thomas Jaszewski

Well-Known Member
This is a Klondike - for unscrupulous Asian suppliers. Put it in, nobody will know as long as it "works" - meaning the motor is spinning somehow. Isn't BMS supposed to prevent such a catastrophic discharge by opening the contacts and shutting itself down too?
There is no industry standard for BMS performance. The best OEM eBike builders use quality, highly engineered products. But those budget bikes, Aliexpress sellers and unpredictable and unreliable. No one buys batteries with regard to the BMS features. Once again, I’ve reported it numerous times. I have batteries claimed to be USA made that have the same construction as UPP and other budget China builders. Guess what? Were lied to.
 
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Thomas Jaszewski

Well-Known Member
I wouldn't sweat it. I've got a battery that has always reported no more than 54.3. How are you measuring?
BTW, it can be a good practice, especially with aftermarket, budget Chinese, and typical batteries from people like Luna, to do a few monitored long charges to possibly better balance the batteries. Especially those with unsophisticated BMS. I have budget batteries, expensive top flight batteries, and better than average aftermarket batteries. They all benefit from a good management plan.

Officially I am a Grin dealer, attempting disclosure here but don’t actively market or sell any volume, and a Satiator user from introduction. For those with less than top flight, and even for best batteries on the market, a sophisticated charger pays for itself. Look, batteries are far more forgiving in use where they are used at lower outputs. It’s when you start running systems at 30, 40, 50 and higher burst amps that things get dicey with cheap BMS and budget builds.

Sometimes those of us with 250-500W systems, operating at 15-25A overthink battery efficiency. As long as the build doesn’t bottle neck power and is reasonably designed, and good management methods are followed, you’re golden.

As always, YMMV, and someone is always more experienced...
 

Alex M

Active Member
One good thing about Grin Satiator is that it can be programmed to start charging at low current, then gradually ramping it up to a certain value. Not only batteries don't like high output, they also don't like high input. We often complain on slow low-amp OEM chargers included with ebikes, but let's not forget that slow charging extends the battery life.