Power problems.

[ICMF]

So, I'm hoping to integrate a power bank into my build. There are a few reasons: I need a bigger battery because of my larger screen; it's cheaper than a powerboost; theoretically simpler; theoretically 'better' batteries vs. eBay lipos that don't meet their specs or will lose charge rapidly.

The problem I'm having is figuring out a way to re-charge the power bank, and keep playing while it *is* charging.

Most power banks seem to have eliminated pass-through (charging devices while the battery itself charges). And for the few that do, common wisdom seems to be that it dramatically decreases the battery's lifespan and should be avoided at all costs. Additionally, most power banks have really low input current, so a GBZ would consume more power than the powerbank can pull in. Meaning the battery wouldn't charge anyway.

And finding a powerbank that is: 5000 - 10,000mAh, with pass-through, with a high enough input current, and an on/off switch, that doesn't use 18650s and costs under $50 is a surprisingly difficult task.

So my current thinking is to use a switched input.

With the switch to the left, it runs off batteries. (~7hr for a 10000mAh battery)
Switch in the middle, it re-charges the power bank.
Switch to the right, it runs off a standard 5V/2.5A power adapter.



Does that make... any sense? Should I have any concerns about the power backfeeding? Or should I just roll the dice and go with some eBay LiPos?

[abrugsch]

how about this... (it's probably not the most efficient but might get you out of a bind...)

use a ~2000mAh + powerboost 1000c which allows playing while charging etc.
but instead of charging it from an external source, have a powerbank between your external 5v and the PB in. that way when the power bank disables output because it's charging, the powerboost + 2000mAh is still supplying the Pi. when the external power is removed, the power bank charges the powerboost.

it's probably horribly inefficient(or maybe not, but you know, 5v->charge, 3.7v ->5v -> charge ->5v again) , but it should work with off the shelf parts

[ICMF]

Interesting idea. Sounds a little bulky though - I can squeeze a power bank in the case, but a second battery would require another layer.

Starting to wonder if I should just bite the bullet and go with an eBay lipo... It'd be nice if I could just pull a battery out of a (reputable) power bank, but I'm fairly certain it wouldn't have a charge protection circuit on the battery itself.

[Will_Temeraire]

I know you don't like the "18650er"-Solution, but you can harvest "good" batteries out of old laptop batteries.
Maybe you want to have a look at Simple Balance Charger - Adafruit. They're using a lipo charger to charge two ("balanced") cells and switch between the two states ("Charge" and "Run") with a 3PDT just like you. Maybe you can use a relay or something like that, to detect wether you've connected it to an external powersupply or not.

Greetings