I thought using Power Tool Batteries was a great idea ... until I had my BlackTip for a while.
Now, I think they have these problems:
If the scooter uses more than 1 (as all BlackTips do), then they can easily get out of balance with each other and you end up having your scooter shut off at very inopportune times. I've had this happen with mine numerous times and my batteries are DeWalt 12 Ah that were bought new, together. They have only ever been used in my scooter and only charged on my DeWalt 4-bay charger. So, they have identical usage and charging history. There is no reason they should ever be out of balance, but I've had it shut down on me several times when I was working the scooter hard (e.g. speed 6 or 7 against the current in the Saint Lawrence River). Maybe I just got a "bad" PTB, but if that's it, then how can you ever trust them? I mean, mine seem to work fine when I just putt around at speed 3 or 4. But, when it's Go Time, sometimes they do okay, and SOME times, they have caused my scooter to just shut off while displaying an indicator of one or the other battery having an issue. I let it stay off for a short time and then it will start up and go again for another stint.
You have to open the hull every time you want to charge the batteries. That kinda sucks. Especially if you are trying to use smaller battery packs and swap between dives. It's not AS bad when the batteries last all day and you only have to open the hull at the end of the day to charge them overnight. Opening the hull is an opportunity to get drops of water inside, which can cause problems (especially if it's salt water), and also it's an opportunity to mess up an O-ring and have a flood.
They are not as space-efficient as custom battery packs. That is why the biggest PTB setup you can put in a BlackTip Tech is 12 Ah, but you can get a custom battery pack for the same scooter from
@Jona Silverstein that is 20 Ah in the same space.
So, after owning a DPV that uses PTBs, my ideal setup would be what the Logic Genesis 2.x and 3.x have. Their battery pack is proprietary, but it uses individual 18650 batteries that the user can replace themselves. And there is a smartphone app that lets you check the battery status and identify if you have one bad cell that you need to replace. At least, that is my understanding. And they are TSA-compliant, so you can fly with them. Right now, my wallet says I can only aspire to own a Genesis.
When the battery setup is enough to last me all day, then using power tool batteries does not offer ME any advantage. I can charge overnight, in which case it doesn't matter whether I'm charging PTBs or something proprietary. It would only be an advantage if the battery did not last all day and I wanted to swap between dives to instantly get back to a full charge.
I have yet to burn all the way through my one set of 12 Ah batteries in a day, so I'm not getting any advantage from having PTBs. In fact, they are a disadvantage because, as I said, I have to open the hull to charge them overnight. That means I'm much more likely to have a flood at some point than I would be if I had a proprietary battery pack in a scooter that supported through-hull charging (like the Genesis and the Seacraft Future, and, I'm sure, others). Opening the hull every night versus never opening the hull at all, unless I need to change weighting from salt water to fresh water (or vice versa).
Going back to the space efficiency issue again for a moment. Because of the form factor, the most I can put in my BlackTip (using PTBs) is 2 x 12 Ah. That gives me (18V x 12Ah x 2=) 432 W-Hr of capacity. A Genesis 2.1 is roughly the same size and weight as a BlackTip Travel (okay, between a Travel and Tech, I think), and it is 850 W-Hr of capacity. Basically, double the capacity, so double the range/runtime. Since I have yet to burn through my 432 W-Hr in one day, I think having 850 would be MORE than enough for me for the foreseeable future. MORE then enough. I probably would not even need to charge a Genesis at all during a weekend of diving. I don't dive caves (yet).
So, what would I want in a new scooter. Well, basically, exactly what a Genesis 3.1 is, with a few enhancements:
A throttle that can be easily controlled with either hand without needing to be "reversed". But, I'll take the current Genesis throttle setup over any other one I've actually seen (note that my experience here is not very broad).
A built-in display that shows all the info the Logic Sentry shows, plus having a leak detector integrated into it.
Built-in cruise control. One that is VERY easy to disengage. Easier to disengage than how I understand the current Genesis throttle lock to work. Maybe even automatically disengage if the tow cord goes slack at all or the prop gets fouled?
Some kind of integrated mount options, so a camera or light mount doesn't have to rely on a cam band to hold it in place. Or maybe that's easy enough to accomplish with hose clamps and not necessary to be integrated into the hull/nose....
Totally silent. I had my BlackTip before the "quiet" firmware. The "quiet" firmware made it SO much nicer!
User-updateable, open source firmware. That is a GREAT feature of the BlackTip.
And then, of course, if it were even smaller and lighter, with the same battery capacity and max thrust, that would make it even more awesome.