

I find this question a lot on the forums. Let's start off with what many people consider the cost of an original brand battery, here for example, a Ryobi 18v 4Ah battery sold at Home Depot...
Wow, that's a lot of money! So, you go to Amazon and find a nice set of 2 knockoff batteries, 4Ah, for half the price of just 1 original Ryobi battery...
That's a much better deal, don't you think? Well, maybe not, and here is why.
1) Ryobi batteries deliver the rated capacity of their batteries, all the time. Knockoff batteries almost always exaggerate the capacity and deliver maybe only 50% of their stated capacity. I know, I have run some tests on my testing equipment at home.
2) Ryobi batteries are under warranty for 3 years. Knockoff batteries typically only have a 1 year warranty, but you might not find the seller of the knockoff batteries listed after a few months. Read the many negative reviews of people trying to get replacement knockoff batteries if they go bad within the warranty period.
3) Ryobi uses new battery cells in their packs. The knockoff batteries are known to harvest used cells from other packs and repackage them for resell.
4) The build quality of the original Ryobi battery is usually much better in terms of soldering, wire used, connectors, etc... compared to the knockoff batteries which use less expensive materials to cut costs.
5) You should never buy Ryobi batteries at full retail price. You don't have to. At least a couple times a year, Ryobi has specials that if you buy a battery pack, you get a free tool. Right now, you can buy a 2 pack of Ryobi 18v 4Ah batteries with charger for $99 and get to pick out a few tool options.
I have been considering getting a new 6-inch pruning chainsaw and that comes with the current promotion. The pruning chainsaw retails for $150.00. But when you get it for free with the purchase of the 2 pack 4Ah batteries, it magically goes down in price in the cart for $60.00, and the 2 4Ah battery combo kit with charger is reduced to $40.00.
Now, how much did you actually pay for those genuine original Ryobi 4Ah batteries? If you were already going to purchase that pruning chainsaw, I guess you say that you both saved $50 on the sale promotion and the batteries and charger were free. If you decided to return the batteries and charger to Home Depot and just keep the saw, you would only get back $40.00.
But we started off with a 2 pack of knockoff batteries, without a charger, selling for $50 on Amazon! So, are you really saving money by buying knockoff batteries? IMHO, no, you can't save money on knockoff batteries if you know when and how to buy the Ryobi tools on their promos.
I suspect the same is true for other brand named tools like DeWalt, Rigid, Milwaukee, etc... The special promotions basically give away batteries to keep you in their ecosystem.

Here is a picture of my battery shelf with some of my batteries ready to be used....