Karl Gesslein says "There are 2 kinds of BMS, ‘balancing’ (smart) BMS and ‘monitoring’ (stupid) BMS. "
https://electricbike-blog.com/2015/02/15/nursing-an-out-of-balance-lithium-cell-back-to-health-without-dying-in-the-process/
Tom Jazewksi (he posts here sometimes) used to do some customer support for Unit Pack Power, and says a lot of their packs use the "stupid" BMS. I have a few batteries purchased over the years from UPP . I also have other packs with balance BMS inside, and they will draw 40 to 50 ma for a while after their chargers go green. My UPP packs don't do that,
In fact, I replaced the BMS in a UPP bottle battery this week. When I opened it up and found all the cells in perfect balance anyway, I almost buttoned it back up, Why break something that was working, but I purchased a balance BMS last summer and forced myself to do it.
Here's the battery. It's made with GA cells.
Tiny little BMS removed from the battery. There's no room for balance circuits on this thing. That's a Canadian nickel next to it. The dIameter of the BMS circuit board is about 1 3/8".
I rounded the corners off an Annpower BMS (with balance circuit) and shoehorned it in. I don't think it will run any better if the original pack was balanced after 2 years.
The install went without incident. I made one error and skipped a cell, but I double check each balance wire with a meter and caught the mistake immediately. Whew.
It also turns out the many of the BMS I see on ebay and aliexpress have no balance circuits.