My shaver arrived yesterday. I’ll use it for the first time mañana.
I bought four cleaner cartridges with the shaver. Amazon sells the four-pack for $17.32. Out of curiosity, and remembering this post, I searched ‘braun’ ‘clean and renew’ ‘ingredients’. I found this page, which recommends using 70% isopropyl alcohol and ‘refill packs’ containing scent and oil. Each refill pack and 500 ml bottle of alcohol fills a cartridge three times. The refill packs cost $22 for three of them, so that’s nine cartridge refills. Alcohol is cheap. The presenter in the video that is on the page said that alcohol costs between $2 and $5. Let’s say it’s $3, and you’ll need three for nine refills. Nine and twenty-two comes to $31. Call it $3.50 per refill. Amazon’s price is $4.33 per refill according to their site for the four-pack. (Or you can just do the math. 
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Considering that it’s ‘futzy’ to clean the used cartridges, order the refill packs, mix the alcohol and refill packs, and fill the empty, cleaned cartridge, I’d rather spend the extra 83¢ and not have to mess with it. The presenter does mention that someone suggested using 42 drops of lemon essential oil per cartridge instead of the refill packs. Lemon essential oil is about $10 for four ounces. The refill packs are 10 ml, or about ⅓ ounce. The presenter didn’t know it, but a ‘drop’ is 0.05 ml, or 0.0017 ounces. Forty-two drops would be about 0.07 ounces. So the lemon essential oil would greatly reduce the price per refilled cartridge. But still too ‘futzy’.
[NB: I went to the website mentioned in the video, and it looks like the price of the refill packs came down to $18.75 for three.)