According to RavPower they say they do have it
https://blog.ravpower.com/2019/09/pass-through-charging-in-2019-update-ravpower-recommendations/
So not sure why you say they dont. I might have picked the wrong model on amazon I need to check that.
I confirmed this one has Pass Through
https://www.amazon.com/gp/B082PGS78L
I'm pleased to hear that RAVpower claims that the product can handle pass through charging. Curiously though, they don't specifically mention the feature on their product pages on their web site but they claim it on their blog site.
In once instance, pass-through charging is only confirmed in a confusing sort of review/FAQ section where a
buyer says,
"For the time I was charging it yes I does. I did notice on the side with the USB ports did get a little warm and haven't done it since. I did this only for the duration of a single charge on my Galaxy Note Edge."
FAQs are usually not provided by customers, especially based on a single use so it is impossible to confirm his remark.
I confirmed this one has Pass Through
https://www.amazon.com/gp/B082PGS78L
On RAVpower's
web site page for this product or on the Amazon link you provided there is no mention whatsoever of pass-through-charging. One has to wonder why RAVpower doesn't tout a desirable feature like pass-through-charging on their product sales pages even though they do tout it on their blog.
For
another power bank on RAVpower's web site, they provide the following answer in the "FAQ" section - (RAVpower's FAQ answers appear to be provided by customers and so they are questionable.)
1. Can you charge the power bank while the power bank is charging another device?
"As others have said, yes, you can do this. But if you are running another device, and you then attach the plug to charge the power bank, the device output will switch off. You can restart it by pressing the button, but this means you cannot use the power bank as an uninterruptible 5V supply. Maybe this doesn't matter for most users, but it caught me out."
So once again, a buyer is answering the question, not RAVpower.
For
this power bank RAVpower does provide a definitive answer in their questions section:
Question: Does it handle passthrough charging? Can I charge a laptop on the usb c output or a phone from the i-smart socket while charging this device?
Answer: yes
They seem to be all over the place with how they claim the feature and it seems to be based on the particular product. Nevertheless, RAVpower is a good company (I own a few of their products) and I think you should be OK as long as you choose the right product.
All this reminds me a bit of the Anker power bank pass-through-charging saga. Early on, like five years ago or so Anker claimed their power banks could handle pass-through-charging but they were vague about whether it was a specific feature based on including the required circuitry. Eventually, they reversed course, and publicly (and repeatedly) have stated, "We no longer support pass-through-charging for our power banks." They now caution buyers that you could damage the power banks as well as the device you are charging.
Anker is a good company that makes quality products but the truth of the matter was that Anker power banks never had real pass-through-charging "functionality" to begin with. One could argue they had nothing to actually "remove" as a "function" as they claim, but nevertheless, I applaud them for addressing the issue and clarifying publicly that their products do not support pass-through.
RAVpower is similarly vague about the feature in that they mostly don't specifically mention it on their sales pages but if they say so on their blog I "suppose" we can trust that, I guess?
For these reasons, if you want to go with pass-through-charging I feel it is best to go with a brand like Zendure where they state definitively right up front with each power bank they sell whether or not the product specifically includes the feature.
Battery University explains li-ion battery charging this way:
"
A portable device should be turned off during charge. This allows the battery to reach the set voltage threshold and current saturation point unhindered. A parasitic load confuses the charger by depressing the battery voltage and preventing the current in the saturation stage to drop low enough by drawing a leakage current. A battery may be fully charged, but the prevailing conditions will prompt a continued charge, causing stress."
So what that means is when you have a power bank that is just below the saturation point (full charge) and you are simultaneously running a parasitic load on it while charging, (like running a dash cam) it will
hover just at, and just below the fully charged state. At this point the charging circuitry begins micro-cycling. This means that the charging circuit in the power bank will begin turning on and off very rapidly as it tries to keep the continuously draining battery topped off and this rapid on-off switching will stress the battery cells, the charging circuit and your device. There is also the issue with stress to the electrolyte in the battery cells involving the electro-chemistry of how lithium ions travel back and forth between the cathode and anode during the charging and discharging process. Charging and discharging at the same time will cause stress and excess heat in the battery cells and this can eventually create lithium metal plating which is what ultimately causes lithium-ion batteries to short out and catch fire. And as
@SawMaster points out there are other aspects of the li-ion charging process to contend with. True "pass-through-charging" prevents any of this from occurring.
For some reason, many people think of power banks as being like a bucket of water with a little hole in the bottom and as long as you keep filling the bucket to keep it topped off you will be fine but unfortunately it just doesn't work that way. Pass-through-charging circuitry basically allows the water in the bucket to drain down a bit before turning the spigot back on. Then, when the bucket of water is full again it shuts the spigot off.
This question of pass-through-charging has been a controversial one here on DCT for a long time and there has been a lot of misinformation and wishful thinking involved in how some members use their power banks. For one thing, even with a true pass-through-charging capable power bank, these devices were designed for
periodic charging of portable computing devices like laptops and cell phones. They were
never really designed to be used as full time uninterruptible power supplies, especially permanently in the challenging environment of an automobile with widely changing temperature extremes along with constant shocks and vibrations. They can indeed work for this purpose but should be approached with caution. Cell link products are a different breed of cat and aside from having all the proper circuity they use LiFePO4 cells which can better handle the stresses of full time use in an automobile.