We're going to try canning some homemade chili with canned kidney beans. Question: Would it be best to add the beans right before canning so they don't get over cooked or do you think there would be little difference if they were cooked with the chili before canning. I'm trying to avoid mushy beans but would like to cook a big pot and can the left overs. I usually add the beans in the last half hour of cooking anyway.
If you are going to be canning this for long term storage you will need to be pressure canning it, and as that will mean some pretty high heat you'd be better off not cooking you beans too long before canning. I'd add them in a few minutes before the end of cooking just to get them warmed up in preparation for canning it as a half hour of cooking plus pressure canning would probably mean mush.
As with all canning endeavors there are several guidelines that dictate how to can chili SAFELY. For starters, as this is a mixture of low acid foods, this MUST be pressure canned. Secondly, regarding the fact that it is chili - when canning chili that contains both meat and beans as you will be doing, you can ONLY safely do so in jars pint-sized or smaller. Additionally, you must thin it out to the point where a spoon stuck vertically into it will immediately fall over (this is due to potential density issues where the heat will not evenly penetrate to the center of the jar when using larger jars or very thick chili).
I misread the question and the following paragraph is regarding DRY beans, I'm leaving it here in case someone else comes along and it ends up being useful to them
Regarding the beans, standard canning directions for beans should apply here - that means they must be soaked overnight, then brought to a boil and held there for 2-3 minutes before being left to soak in the hot water for another hour. At this point they will not be soft enough to eat but they are considered "fully hydrated" for the purposes of canning. Regardless of this though they will still soak up more water during the canning process and while being in the jars so I would suggest to thin the chili even more to account for them soaking up some liquid.
If using canned beans then you can probably just mix them in right at the end before adding it to the jars. I think it does need to be a "hot pack" into the jars, so as long as the canned beans warm up to the temperature of the hot chili they should not need any further cooking prior to canning.
For best bets regarding safety with this, stick to this recipe and processing instructions (or at the very least, try to stick to the bean/meat/liquid ratio): http://nchfp.uga.edu/how/can_05/chili_con_carne.html
NCHFP is a trusted website to provide safe and tested canning instructions. There are a LOT of unsafe practices flaunted on youtube and pintrest so its important to always check things against a tested source.
It should also go without saying that the standard non-cannable list of things still applies, to safely can this you cannot add any form of thickeners: corn-starch, flour, etc. (this also includes things like rice and pasta although I don't know why that would be in a chili :) ), its also better to avoid adding as much fat as possible - butter/oil, and if you can drain the fat off the meat after it is cooked. Dairy/eggs is also not safe to have in canned goods in any amount, this would include cheese and milk/cream. (Not sure if most people put this in their chili but I do so thought I would mention it)
Safe canning! :)