I love the PB2 but the inability to charge low drain devices is a bummer. If I had known that before hand I would have never bought it. Oh well, it charges the wifes cell phone when she is out and about for the day and it does charge a few particular 18650’s quickly. Other than that, it’s useless.
PB2 will turn off when output is lower than (I think) around 300mA. So charging the smartphone is fine as it has high current for fast charging, but some devices use low current (for low capacity battery) and it will not work with PB2 as power bank… Deal breaker for me too, I would have two PB2s already at home if it does not do this…
Does it feature independent charging? Meaning the 2 batteries are in parallel or separate? (what I mean is, if they are in parallel, then it may not be good to charge 2 different capacity batteries or 2 batteries in different state of charge (different voltage when first placed inside that powerbank)…
The Xtar PB2 has independent charging. I believe many of the Tomo (2/3/4-bay) powerbank/charger models also have independent charging.
An inherent problem with removable cell power banks is contact resistances (springs, contact themselves and etc). They pose an efficiency and to some extent cut-off hurdle which increases with current draw.
Power bank circuitry works much better when batteries are soldered (low temp solder solutions available) or spot welded.
Thanks for the additional explanation, but I still have some questions…
Assuming 2 batteries (in the above parallel-type powerbank) have different capacities but same voltage, then it’s safe to use in the powerbank, is that what is meant?
But if 2 batteries have a big voltage difference, then that’s a no-go, since (from what I understand), the higher voltage battery is going to “charge” the lower voltage battery at a possibly very fast charge rate. But what happens if this has been done? Will the batteries spark or explode? Or its just going to shorten battery life? Or do some other not-so-good thing (like damaging the powerbank circuitry)?
Of course you can avoid that by measuring battery voltage with a multimeter or battery charger. Nothing very wrong can happen anyway since the current flow will be limited by the sum of both cells internal resistances plus contact and spring resistances, and the initial current inrush soon tapers very much like the current tapering which happens upon entering CV phase during a standard charge. If you witness sparks or fumes out of the circuitry upon cell insertion you are either inserting a cell in reverse :facepalm: (DO NOT!) or cell voltages are too dissimilar. Better avoided but no big deal.