Replace rear pannier battery


New Member
United Kingdom
I've seen rear rack batteries (with or without the fitting rear pannier) on Ali express with free delivery with 36v 20Ah (giving 42*20=840wah when fully charged?). They claim to be Samsung/LG cells.

Could I buy a second hand step through e-bike with rear pannier battery and replace the rear battery/ pannier ? If it's the same voltage but larger capacity will that be a problem? Where is the battery controller generally - is that part of the battery housing ?

There are thousands of **** batteries for sale on aliexp, ebay, amazon. I bought two. Warranty doesn't mean much when you are prohibited from shipping the battery back by UPS, FedEx, Royal Mail. I got money back from Amazon for a battery but I couldn't prove the Ebay battery bad in 30 days to get money back. What cells don't matter if the vendor can't make good welds between the cells. Neither of the bad batteries I bought could climb a hill without the voltage collapsing. Went from 53 v to 7 on the Amazon, stayed there. Went from 53 to 11 on the ebay one but would bounce back immediately when the throttle was turned off.
For replacement Increased capacity doesn't matter. Same voltage range (36, or 48) does matter.
Controller location depends on the bike vendor. Batteries with an IC in the battery to communicate with the controller cannot be replaced except original brand. Tipoff, more wires to the battery than four: two for the current to the controller, two to the charging connector.
Buying the battery from reputable vendor is what I eventually did. That battery is 5 1/3 years old, works fine. Cost twice as much as the trash batteries. I don't known what vendors in UK are reputable. Reentron In Shanghai and Em3ev in Hong Kong have good reputations.