Tool batteries, let alone marine batteries, would tend to violate the OPs criterion of "smallish".For off the shelf stuff you have Power tool batteries + buck converter.
Next step up from there are deep discharge boat/wheelchair batteries + buck converter
I think the real problem is that far too many people severely over estimate the energy capacity of batteries. The only general solution I can see (and it won't be cheap) would be development and marketing of small fuel cell units. I've been seeing articles about that for years. The idea of having a fuel cell powered cell phone, for instance. Then the only concern will be power that such devices can deliver as they'd be able to deliver the power for as long as the hydrogen supply holds out.
Statistics: Posted by W. H. Heydt — Mon Mar 11, 2024 12:20 am