More than likely the battery has developed a memory. Ni-Cad batteries are worst for this kind of problem, but other than Ni-Cad batteries take much longer for the problem to occur. years ago there were all sorts of chargers/maintainers one could use to discharge and recharge the battery several times to correct the problem, but nowadays it's just as easy to buy a new battery and be done with it. A battery should give you about a year of good use.

That battery should be a lithium-ion battery, and, therefore, much more resistant to a memory effect than NiCds. But ray is right -- this battery likely is spent. Two days standby is not much, especially if you don't have analog service on the phone. It's easiest to get a new battery. I've purchased several batteries off that big auction site (even third-party non-brands) and, if you're careful to buy from a seller who makes their living selling phones and accessories, you're likely to get a decent battery for not much money.

I have an old Kyocera QCP 3035, which is having the same problem. It doesn't hold a charge for very long. Where can I find a replacement battery, and how do I install it?

eBay