If you have the technical background to have an informed opinion about aftermarket tool batteries, or if you have substantial experience with them, please share your opinion of their quality: either specific brands (I need an 18v Ridgid battery) or in general.

I'm reading reviews. The user reviews are about what I'd expect: some enthusiastic, some disgusted. Few if any complain about a battery damaging a tool.

The professionally written reviews seem to be unanimous that all aftermarket batteries are unsafe. Ordinarily I'd accept that and pay the (substantial) premium for an OEM battery, but a couple of things make me suspicious.

One is that most of these reviews appear to be written by people with an imperfect mastery of English. There are misspellings in the text and even in the content summaries that Google displays. Everyone who knows their topic is not necessarily a good writer, but any web site that publishes professional reviews should have a competent editor who cleans them up -- if it's legitimate.

My other suspicion concerns the reasons these reviews give, which often seem vague or specious. For example, one says that modern power tools and OEM batteries are programmed to work together, and aftermarket producers can't duplicate the programming. The example it gives: if you run a tool flat-out for a while, the battery should be aware if the motor is overheating and shut down before it is damaged. I'm not an expert in this field, but I can think like an engineer, and that sounds bogus. Maybe tools batteries do have programming, but no sane engineer would make the tool tell the battery that its motor is overheating and expect the battery to shut down. If the tool needs to shut down to protect its motor, it should shut down itself. It's a matter of design simplicity and economy, as well as safety: why duplicate circuitry in every battery when you can put it in the tool, where fewer units are needed and they can be better protected?