Things are not adding up.
You can use a slow card in the camera and it wont damage the camera. You wont be able to achieve the camera's peak performance... but it isn't going to "damage" the camera.
The camera has an internal memory buffer which is MUCH faster than the card's write-speed. When you take a shot, the image is temporarly saved in the camera's internal memory buffer and the camera is immediately able to take another shot. WHILE that's happening, the camera will save the image in the internal memory buffer to the card.
But if you take many shots in rapid succession... you'll fill the internal memory buffer and it wont have enough room to take another shot. When that happens, the camera will display "busy" and it will not let you take another shot until it can free some buffer space as it saves the image data to the memory card. A slow memory card just means that it can't write very fast... so youy'll wait longer for the buffer to clear. But it wont break the camera.
If you try to use the camera for video... you may find that the camera can't record very long before it stops... because the buffer filled and there was literally nowhere to store the video frames. Card speed is especially important for video.
As for the battery. I only use genuine Canon batteries. But Canon's batteries are Lithium Ion and Lithium batteries don't leak. In cold temps they don't freeze (that have an especially cold freezing point). Some Lithium polymer batteries have been known to catch fire (and make the news... noteable on some cellphones and laptop computer batteries). But I have never heard of such an indcident with a genuine Canon battery (part of this has to do with how the battery is made.
Batteries work by having an "annode" material and a "cathode" material that do not directly touch... except for an electrolyte material (such as a solution, a gel, etc.) which allows electrons to flow from one side of the battery to the other.
If the annode & cathode can directly touch, then the rapid transfer will generate massive heat and the battery can cause burn damage, start a fire, etc. (your camera wasn't burned nor did it catch on fire, did it?)
This becomes riskier in higher capacity batteries because the manufacturer tries to add more layers of annode & cathode material in the same amount of physical space. This makes the layers thinner, closer, and the risk of damage is higher (and the potential for catestrophic results.) This is why ... when someone advertises their battery has a higher capacity than the manufacturer's original batteries... I am NOT inclined to buy them. Canon designs their batteries to be safe for their own products.
Alkaline batteries (which is not what Canon uses) have a different problem. When those batteries are completely deplete, the batteries may actually leak. The leaked material can result in corrosive damage to the electronics. You would physically see that corrosion (it would be very obvious) by looking inside the battery compartment.
If the batteries put out proper voltage, did not leak, and did not create excessive heat... then it's pretty hard to imagine the battery could possibly damage the product.
In other words... I am extremely skeptical about the service center's claims and suspect the person who inspected your camera was not qualified to diagnose the issue.
There can be loads of reasons why cameras fail. Also, Canon has a couple of mini switches which will prevent the camera from powering up unless they are engaged. One is in the battery compartment door. The other is in the memory compartment door. Both doors must be completely closed or the camera will not power on. If the door is damaged, this would be a problem.
I HAVE encountered cameras where the switch was flakey and not completely engaging even when the door was completely closed. Sometimes the plastic is a bit warped and not fully engaging (pressing the door tightly may cause the camera to wake up. But as you probably don't want to have to run around continuously applying pressure on the door to make the camera work, you'd probably want to get the door replaced if this were found to be the problem.)
Cameras can also have internal defects ... a wire harness that came loose. A damaged board. If liquids managed to get into the camra (especially salt-water ... which is paticularly bad) then that can damage the camera.
As DSLR camera prices go... the 1100D is a low-cost camera. Since most of the cost of the repair is the amount of labor and labor hours are epensive (more than the electronics), it may not be worth the high-cost of repair and the money may be better spent on a new camera.
Advising against the repair of an older model entry-level camera is probably good advice (I wouldn't invest in the cost to repair it... especially since you don't know what else may fail next. Shutters are expected to wear after enough use and that could be another expensive repair.)
Tim Campbell
5D III, 5D IV, 60Da
