First guess was, bad battery. Nope, I tried four that are all fine in other ##-D cameras.

I was thinking high battery usage, something draining them fast? Nope, put them on the charger and in under a minute full charge. Edit: now the second two batteries are taking longer. Of course if two are old, and recarge fast, short life, but two are newer and take longer to re-charge... I'm back to the camera is draining them? 

I'm guessing now that the camera is registering low power and shutting down, because of an error in the hardware or software that reads the battery voltage. Before I send this in to Canon, anyone have a similar experience or advise. I'm thinking I can maybe pull the system battery and leave it for a complete reset.

I did some searches, so far only found people with drain problems, non-Canon lenses or while the camera was off. I haven't located anything where fully functional camera, gives false battery low reports.

I don�t know if this is a help but I had a 50D and there is a tab on the battery door that got mashed down, it controlled a microswitch. That gave me similar issues. I bought a replacement door from Canon then all worked ok.

Thanks for ideas.

Also I noticed the LCD is flickering sometimes, which I never saw before. Meanwhile I tried a total reset, no change. Now I'll look at the door and firmware updates. If nothing else, it's going in to Canon.

Camera works. I just shot a 50 minute session, pocket full of batteries.  One went dead, swapped and drooped the old one into a different pocket. I have about 16 batteries because I still use the 10-D, 20-D and just had a 40-D go ERR99 frozen shutter.

First question - are the offending batteries Canon originals? Like proper originals, not fake genuine ones from eBay? Only ever had problems with "cheap" third party batteries. I've had LP-E6 that are old, from the Canon 5D MKII still going strong. A cheap "Jupio" that I got for free can go funny at times and show up as no juice in it - but swapping it's place in the battery grip and it comes back as full - never happens with the Canon originals though. Only every buy proper Canon batteries now-a-days, and not from marketplaces where they potentially could be counterfeit. I think it is a voltage issue, that lesser quality ones doesn't gives out or stable enough voltage, leading to underestimation of its capacity.

Secondly - you can check the health of the battery in the camera's menu systems - at least on the 5D MK IV.

Otherwise, I would try and properly drain it, try to get it as close to genuinely empty as possible and then charge it.

Good Luck!

Thanks both. I have a mix of real and "fake". And true some of the eBay batteries are weak or flat out lies. I mean they will promise 2500 mAh when they might be 1800, and the standard batteries are 1390 mAh. I've had a battery for different equipment, expand, while the real Canon keep their size.

Although I haven't had fake batteries that were so flawed and have had good results over many years with the BP-511A copies. The problem is finding a supplier with good quality vs the ones that are pedaling junk with false claims.

Back to the actual answer. The batteries were from assorted years (yes I mark mine when I get them, so I know) and some came in used cameras, some were mine. Also sometimes sets of batteries sit for months unused, until an event, where I charge everything before I leave. I'm not sure if cycling batteries makes any difference anymore with new battery types like it would have with NiCads. NiMH are less affected. However, low voltage can possibly be corrected by a deep cycle. YES

Newer batteries also have a life of up to 2000 charging cycles. The BP-511A is Lithium-Ion

Since these batteries are old or new or other sources, I don't know what charger someone else used. Heat is the enemy. If they over charged or fast charged, the batteries could be ruined. Mine I only charge in a Canon charger. What I'd really like is a smart charger, which I should invest in, some day. I keep putting it off.

The reason i was kind of closing the thread was, I bought four new batteries, on eBay, and the problem is gone.

Note, I always have IS off unless I need it, kind of opposite to many people. The working and adjusting makes the shutter lag longer, I want as fast as possible. I try to shut off the camera rather than dangling with it on, and view is 3 seconds. Anything to save battery life, especially when I'm up a hill and a mile or more from more. Always have two spares in my pocket and at least one more memory card.

Another problem, which I create, is saving things. With the analyzer I could see the actual values and "get over it" and throw the old worn out batteries away. 

Good that I was reminded, time to go shop for what I should have purchased years ago.

Not much luck finding one for camera batteries.