How detailed should one make a battlecard/killsheet?

I'll try and answer each of these three questions separately.

• My philosophy is short and sweet. If you're making battlecards longer than one page or using size 5 font it's going to be impossible for your sales reps to get the high impact at a glance insight they need. Battle cards work best when they are reference docs a rep can use to find what they're looking for in <30 seconds. If they get lost in the amount of detail you provided, they will not use the battle card after the first attempt.
• If you don't know the technical components and there's no way for you to learn them via kicking off a project to do so, the best thing you can do is shift the story. PMM's value to the business is about being able to find the most compelling story possible within the limitations of available information and the market situation. What do I mean by shift the story? Don't compete with your competitor on their terms. Figure out where you do better -- a certain type of customer, a specific use case, a level of service you provide, a brand identity that resonates with the market you're targeting, etc.
• You ALWAYS have enough to guide sales in some manner. Per my answer to (2) above, PMMs are masters of the story. Sometimes your story will be stronger than others, but some story is better than no story. Work with sales to set expectations on what is realistic given whatever limitations you're facing and test your early drafts with top reps and managers to get feedback on how to improve.

Details on the battlecard really depends on the complexity of the product, solution and industry segment. 

Start with something simple for Version 1 - and as you get more questions / feedback from sales, add to it. While I have done battlecards, they very soon become outdated, so pretty layout etc, goes waste. 

I would really prefer a live FAQ type format that sales can use - searchable on specific topics, competitor, objection handling. 

I have not yet seen tools that can make life simple. Very underserved market. 

(1) I think beyond short and sweet, a battlecard or kill-sheet should be tactical. Literally the format should be: "show xyz when you are stating abc, in this zyx situation" 

(2) Framing to sales that competitor research and battle card development are a team sport. (a) Stuff that you don't know, set expectations with sales where they there are gray areas, and will need their ears and eyes in the market place to find the answers. Of course, you will want to emphasize that you're doing your part to continue to looking into areas where there are limited info. (b) you can/should shift the narrative in the market to focus on your strength. Remember either you create the narrative or you're part of someone's narrative .

(3) You ALWAYS have enough to help the team. My rule or question that I ask myself is: "does this narrative or playbook meet the standards of the top sales people. Is this narrative or playbook their general playbooks and narratives? And will the new, younger, and inexperienced sales person adopt this playbook or narrative?" The answers to all the above questions should be yes, if you can meet these requirements, you have built enough to gude sales. 

I prefer FAQs but more importantly traps and responses. Rather than a encyclopedia, I would create something actionable. 

My philosophy on battlecards aligns well with what the other posters have said on the topic. I tend to create two resources: one that is tactical in nature and gives reps the actual words they need to say in the moment (a true "Battlecard"); the other is more educational and provides deeper exploration when the reps are not in the moment (more of a "Competitor Profile").

If you want maximum traction with sales, you should consider doing these happy paths:

1. Ensure that your battlecards are up-to-date and put them where your team "lives" virtually; as soon as they're unreliable or inaccessible, they are dead.
2. Create opportunities to collaborate with sales, collect feedback on their usefulness, and capture new intel that they're hearing from prospects.
3. Cultivate your power users, capture their success stories, and use them both to promote the value the rest of the sales organization; you should market to sales just like you market to your customers.
4. Be transparent and aggressive about the answers that you don't have and need their help to get from customers and partners; when you get an answer, trumpet that win back into your internal marketing efforts.
5. As you grow the effort, segment information and competition as much as you can; BDRs need different intel than Sales, and EMEA sees different competitors than APAC.

If you aren't partnering with sales, and seeking meaningful feedback from a number of the highest performing reps and sales leaders, I think it's impossible you will get it right. You need to ask sales what they need to know to feel confident. I'm convinced that competitive intelligence as a sales resource is as much about instilling confidence in sales as it is with informing any specific deal strategy. 

That confidence comes from being able to anticipate the landmines their competitor will place, and have a concise response to each. It comes from knowing the competitors product at least well enough to be able to position their own differentiators accordingly. It comes from knowing they can make a statement about the market without fear that they will get egg on their face and lose the confidence of their prospect. 

I think you will never know for sure that you have enough to guide sales, but you should publish anyway. Sales will help you know what's missing, and you can iterate. Avoid battlecards being downloaded locally by reps. They will always have outdated information and the egg on the face will be unavoidable.