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Portable rechargeable battery pack with state-of-charge meter and can be charged while in use? Answered

I've been looking about for something like this, and have yet to find something that will work for my needs. I plan to break ground on a portable Raspberry Pi system, and will need a battery system for it. I've seen a few others around (both RPi portables and battery packs) but I would love to be able to make a battery pack that I can charge while the battery pack is being used, along with add some form of meter to know how much charge I have left.

Any and all help is greatly appreciated!


What sort of batteries were you planning an using? You should be able to charge most battery systems while they are in use, although you may want to look for more information on properly charging lithium batteries if you are using them.

For showing battery voltage, zenner diode can be used to light LEDs at different voltages. Alternatively, you could use comparators to compare the battery voltage to a reference and turn on LEDs when above or below a given level.

That.s the thing: I don't know. I would love to be able to have about 4-6 hours of battery life for this project but I have never touched a battery in the sense of a customer pack.

As for the indicator,thanks! I was able to find quite a few schematics for zenner diode indicators.

You need to find the correct voltage to power the project, and the average/peak current draw. Use average current * run time to get the minimum capacity you need, and you will need the peak current when selecting a battery and voltage regulator.

What sort of batteries did you want to use for this? car/motorcycle batteries and NiMH or NiCdpacks are fairly straightforward to charge, have a high maximum current and are relatively cheap. Lithium batteries require a more complex charger and you will need to watch the temperature to prevent any fires, but will be a lot lighter.

The systems has two power needs: the RPi will run on 5v (not sure, but I know it's lower then the screen) and the screen which will need 12v.

After some basic (and I mean *very* basic) looking, I think I'll be quite fine with NiMH batteries. I've seen a few people make battery packs using standard 10 or so AA. I'd also be fine with using some RC car packs. But again, I'm rather dense when it comes to this.

Yes, pack of 10 1.2V NiMH should work, giving an output in the region of 12V. Battery packs intended for power tools and RC cars will work well, and should be good for at least 10A.

As long as the RPi and anything else using the 5V line are drawing less that 1A, you should be fine with a normal linear regulator with a large enough heatsink.

As the display needs 12V, one would assume it is intended to be used with a car battery, so shouldn't need any additional voltage regulation, although if you can find the specification, it would be a good idea to check the maximum input voltage.

That actually managed to answer just about all my remaining questions! Thank you so very much!

However...if you don't mind me asking one more quick question here...how would one set up the plug for the charger for a 10 AA battery pack? And how would you wire the charger and plug?

The charger just needs to be connected across the battery pack. Unless it's putting out more than 14V when connected, you shouldn't have any problems.

In theory, all you need to charge the battery pack is a voltage a little higher than the normal output voltage. If you're building your own charger, find an empty battery and increase the applied voltage until the current flowing into the battery reaches a suitable level (depends on the capabilities of the charger, but I wouldn't go much higher than 2A).

I haven't got too much experience with charging batteries, but NiMH charger circuits should be fairly common, and it would probably be a good idea to find a suitable one and adapt it to output the correct voltage. (Alternatively, commercial chargers are fairly cheap second hand and have relatively little that can go wrong)