Instruction: Answer the given question using the supporting document.

Input:
Question: Charger's output is 4.2V 600mA, how can it charge the battery to 7.4V?
Document: This is a great quality battery and charger. The charger charge the cannon battery too. It lasted almost 2 hours. Price can not be beat.
Make sure, as with all lithium batteries, you charge it up all the way when you get it, and then immediately discharge it all the way. Put your camera on a tri-pod or something and have it record until it runs out of power. Then recharge the battery again. This will ensure proper calculation of battery life. Once you do this once, you can recharge it at any time !! !
I am happy with this battery since my Canon is dying and can't hold charge that long. Even at full charge it can only power the camcorder for less than 20 minutes. This Progo lasts much longer. The charger has something loose in it as it rattles around, but doesn't affect the battery in any way.
Works as advertised, however, I don't know if it was my unit only that I cannot charge the original Canon battery using this charger, and this battery after the full charge shows 155 minutes for recording, (kind of disappointed for such large battery(it is more than twice of the original battery came with the camcorder)). But for the price and functionality, nothing beats it, highly recommended!
My 2009-era Canon Vixia HF S11 recorded got to the point where I'd be lucky to get 25 minutes out of the stock battery pack; it just wouldn't hold much of a charge anymore. I bought this about a month ago and now it's back to beyond what the factory battery originally did since this one is slightly larger than the mAh rating the stock battery is.
Before buying this kit I had read reviews for some other replacement batteries where people were complaining about compatibility and the remaining charge time not showing up on the cameras. This one works as described in my Canon HF-M40 camcorder - I get adequate charge time out of the battery, and my camera displays remaining time. Only had it a week so far, so we'll see how many charges this thing is good for.
I had read several reviews about people having issues with third party batteries not being properly recognized by their Canon M41. After looking at the various battery vendors and options I decided to take a chance with Progo (Maxtek).I initially purchased their BP-827 equivalent battery, based on one customer review. This battery was recognized by my Cannon M41 without any issues, battery life is reported properly and I can charge the battery without issue.
This package was exactly what we needed before we left for our vacation. It's nice to have a spare battery and not have to carry around the long cords and charger that came with the camera.
This fit perfectly and has worked well since we got it! We received a canon camera without a battery, so glad I found this one and it worked out well!
The charger appears to be well built and charges the OEM battery (short), the included battery (medium), and a different after-market battery (long) that I own for my M40. time displays on the camera, and this battery (medium) is flush with the back of the camera.
Answer: Looks like a typo, on the back of my charge unit it says input 100v-240v max 150mA, or DC 12v-24v.  Output, DC 8.4v 600mA.