Little covers, screws, coin slots all cost money either in parts or the cost of the tooling to produce those parts and as mooly says, the life of the battery is much longer than the warranty. When the manufacturer is designing his latest laptop one of his criteria will be to make the design easily upgradeable so that model variations using the same tooling can be produced. That means easy access to the memory and the hard drive, possibly the WI-Fi card for models with and without Bluetooth. Those justify the extra parts and tooling costs. The last thing on his mind will be the placement of the CMOS battery which will be situated on the motherboard for convenience to associated circuit parts and for easy assembly on the production line. Just about all motherboards use the same type of battery so variations from model to model do not have be catered for and there is no money in it for the manufacturer in supplying replacements for exhausted batteries several years down the line. Just like cars, laptops are designed for a price point and the design is governed more by what is best for the manufacturer than what is desirable for the end user. It all boils down to money in the end; when comparing laptop features would you pay more for a model with a replaceable battery cover? I don't think I would.