I have a Canon G5 and am on my third set of rechargeable batteries (I bought an extra Canon rechargeable battery when I purchased the camera and then 2 Canon brand replacement batteries when the first 2 failed and then 2 off brand replacement batteries when the 2 Canon replacements would not work). The following has happened with each set of batteries: The original two Canon batteries. After about a year or so of perfect performance a day came, after getting a fully charged indication on both the original and extra battery, the camera would turn on, take about two or three pictures, indicate low battery and then shut down and not start again. The same thing happened with both batteries on the same day. The camera worked perfectly when directly connected to electrical socket. The two Canon Brand replacement batteries: Immediately upon receipt of both the new Canon replacement batteries, after getting a fully charged indication on both the replacement batteries, the camera would turn on, take about two or three pictures, indicate low battery and then shut down and not start again. The same thing happened with both batteries on the same day. The camera worked perfectly when directly connected to electrical socket. The two off brand replacement batteries: Upon receipt of the replacements, after getting a fully charged indication on both, the camera worked perfectly for about a year until a day came that, after getting a fully charged indication on both, it would turn on, take about two or three pictures, indicate low battery and then shut down and not start again. The same thing happened with both batteries on the same day. The camera worked perfectly when directly connected to electrical socket. This sounds like a camera issue rather than a battery issue. Please let me know what you think.

Thank you for such a detailed description, wishing others would take your lead. To the problem camera designated batteries (other then AA rechargeable) have always been a bit of a sore spot for me because the user is compelled to purchase a specific battery. As much as I prefer the name brand accessories for the camera there come a point where you just gotta venture forth with third party accessories. There is nothing wrong with using an "off" brand in fact what I've found is that is some cases they are a better battery. Again back to the problem. I grasping thoughts on how to word this but, here goes. As much as the manufactures would like you to believe that these batteries do not form a memory they do. Also the battery can trick you into thinking it's fully charged when in fact even though the charge light is saying completed it's only got about 1/3 charge. I've worked with Canon's BP 511 and now the "new" BP 511A for many years The BP511A or equivalent is the better battery. What needs to be done is to drain those batteries down until they stop, let it cool don't take it from the camera to the charger. Time the battery when you put it on the charger, meaning not to the second but what you would "normally" do is plug the battery into the charger and leave it right. Well what's possibly happening is that within ten minute the ready light is coming on, (something stupid going on in the battery) So check the battery stat of charge after say 15 minutes and if it says it ready (drum roll please) remove the battery unplug the charger for a few seconds and place the battery charger back onto the wall outlet and plug the battery back into the charger and look at your watch again. I've had to do this as much as three times until the thing would get the idea it was to take a charge "normally" about 2 hours will bring it back up. There is no device I've found to completely drain one of these batteries so over a period of time in your case one year the batteries begin this fit. I've since replaced the BP511 for the better BP511A's or equivalent. I'm not pointing a finger because myself and staff do the same thing and pull the battery before going to a shoot if it's showing partial discharge and the thing gets put onto charge and we start this cycle all over again. Be careful of the charger as well meaning don't just disconnect the battery and put it back on charge when it's going the cycle thing disconnect the charger from its power source as well because it holds a memory for a few seconds and will just shut off in a few moments if you don't.

Long story but I've been doing this now for 9 years since the dawn of Canon's 30D Cheers