My first post here so welcome everyone and thank you for the information I have already read in this forum
Reading the comments about RG300, I noticed that a lot of people are worried that BP-5L battery from RG300 is not the same BP-5L that you can buy. The problem is, of course, the contacts in the wrong place, but there is a solution (or even several). The simplest thing you can do is use the battery from the Samsung Galaxy s2. I must point out that I did not care about larger capacity, but about finding a battery that can be replaced quickly. The modification is simple and allows you to use both the Samsung battery and the BP-5L that I got from the RG300.
As you can see in the attachements, the Samsung battery is wider and shorter. For this reason, you need to cut about 90% of the left side wall from the housing and a small pin near the contacts. In addition, using hot glue and a piece of plastic (cut from the DVD packaging) I made the missing wall, only moved by about 2mm.
Because not all of the original plastic has been cut, the Samsung battery does not slide backwards, but it is safer to put something in it - e.g. a piece of rolled paper. In addition, because of the remain fragment, the original battery does not move sideways.
Battery: Samsung Galaxy S2 battery has 4 connectors, but we'll be using only first 3 of them: +, 0, - which are almost in a perfect place. I've scraped the metal from the fourth connector (so it doesn't exist anymore) and removed the plastic from between 3 and 4.
Original Samsung Galaxy S2 batteries are 1600mAh but you can find 1800-2200mAh versions.
(You make all modifications at your own risk, I am not liable for damages if you damage your RG300. It took me about 20 minutes.)