OK - so this isn't plumbing related specifically but is trade related, and may help someone who uses Makita cordless tools.
I have lots of Makita stuff and therefore need lots of batteries. So when one died recently, I popped to buy a new one. Toolstation are selling the new 4ah batteries for about £85 which I know isn't super cheap, but when you consider it will definitely be genuine and that until last month Screwfix wanted £149 for a 3Ah it seems a deal.
So I bought 2 of em. When they arrived they wouldn't fit into any of my 3Ah tools. I quickly realised why, and with the Dremel sorted it in under a minute. The 4Ah isn't going to damage my tools just last longer than a 3Ah. So don't worry about that.
Attached are some photos. I hope this is clear, and it may help someone!
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PS - so far the 4Ah batteries do last a fair bit longer than the 3's.