Maker Pro
Maker Pro

replacing two D cells with pair of 18650 batteries but need voltage drop

Tenergy makes a LSD 9V so that's what I'd get if you want to go that route, but personally, my only 9V devices are some hardwired smoke detectors and a couple clock memory backups, so I just use alkalines because their 10 year shelf life is near what I get out of them. In that case I buy the bulk amazon basics alkalines.
https://www.amazon.com/Tenergy-9V-R...-Self-Discharge-Square-Detector/dp/B003QUNYQI

However I don't even use them in smoke detectors much these days because those now (in the brand that matches what I have (mounting plate)) come with a battery, plus I don't have a charger capable of ~9V cells so it would be a significant investment that takes decades to recoup, longer than the rechargeable batteries' expected lifespan.

I've been intending to check out some youtube videos of the new breed of Li-Ion based 9V, to see how they're coming along. Not sure if those all use a series pair of Li-Ion cells for 8.4v peak, or if they have a boost circuit, to make 9V from ~3.7V. Heh, I'm not in a hurry to spend time on that because I have plenty of spare amazon basics alkalines. They've gotten more expensive though, currently $12 for an 8-pack, were only $10 a couple years ago.

https://www.amazon.com/gp/product/B00MH4QM1S
 
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