Buying Chinese batteries is a minefield. Experience has been that they rarely meet specified capacity, and less that 10% of specified capacity is not that unusual.
So, with that background I searched eBay for replacement batteries for a Makita drill / driver. The current pair of batteries are Chinese source, purchased about 5 years ago, label rating is 2.0Ah, and measured capacity now is 1.3-1.4Ah… which is not too bad, they were 1.7-1.8Ah when new (yes, below spec).
There were very many sellers selling a lot of two packs rated at 3.6Ah for around $34 including delivery. That is very cheap, too good to believe? Let's rely on eBay Buyer Protection to put them to the test.
The two batteries arrived quickly and were put through charge / discharge cycles to condition them.
Above are the C/5 discharge curves for both batteries on the third cycle, capacity is 1.3Ah, just 36% of the label rating.
The pack is probably built on Sub-C cells, and the best price I can quickly find for 10 Panasonic 3.05Ah cells is over $100, so that does not look too good.
A reputable brand of after market replacement battery rated for 3.0Ah is priced at just under $100.
In terms of bang for buck, these are both around $33/Ah capacity, and possibly longer life than the purchased batteries
The cost of quality cells raises the question of whether the purchased batteries are good value if they were honestly rated at 1.2Ah.
The answer is yes (unless you need the longer endurance in a single battery)… but they were even better value.
I raised an eBay dispute since the goods were not as described, and offered to accept 60% discount as compensation for the fact they had only 60% of the paid for capacity (3.0Ah), costing around $5/Ah.