Battery cost logic - If there was a standard for tool batteries, anyone could make those batteries. People would buy batteries on cost rather than being tied into having to buy batteries from a single supplier. That would lead to lower prices. Prices should be lower just because there are more options available within the marketplace. That's the way markets work.
However there is another consideration: If you are a battery tool manufacturer, when you work out the pricing you probably have a calculation which is something along the lines of: "when someone buys a battery tool I will expect over the life of the tool to sell them 2 to 3 batteries, so my income will be bare tool + (3 x batteries). So say each is £50 (for example a basic drill with 4AH batteries), that's £200 income over the life of tool.
At the moment, there is some incentive to hide the longer running cost by dropping the initial cost - which is what most people look at when thinking of buying a tool - and then look to recover the lower cost by bumping up the renewalables cost. So for example, you could sell the base unit for £40, and still gain the £200 total by increasing the battery cost to £53.33. That is likely to result in more sales without losing long term income.
However, if anyone can make the batteries that calculation goes out of the window. If the tool manufacturer can no longer rely on getting income from the batteries they will need to get more income from the tool itself.
To understand that perhaps we need to add another couple of numbers - cost of manufacture and profit. Let's start by assuming that it costs the manufacturer £40 to make each product. If they sell at £50 that's £10 profit per item. So for £200 income recouped by the manufacturer over the life of the tool and its batteries, they make £40 profit. But that's assuming they are sure to get the income from the battery sales!
If the manufacturer is to maintain the £40 profit from the total tool sale when they cannot guarantee income from the batteries their only option is to try to get more profit from the initial tool sale. The easiest way to maintain the £40 profit while competing in the open battery sales market will be to push the price of tool up to near £80, and the batteries price down to close to £40.
Therefore one outcome of cheaper batteries is likely to be more expensive tools. Though it is also worth pointing out that the overall cost to the customer (tool plus batteries) will be the same. Personally I'd prefer the cost to be more upfront with less of what I'm paying to the manufacturer being hidden in inflated consumable costs.