I'm not going to directly tell you which battery to use - but I AM going to say DO NOT put the screen and Pi in series - you'll kill the Pi or possibly them both!

The same battery CAN supply both power requirements - just use regulators to give the 5V supply (The 12V can come directly from a 12V battery).

If you use a higher voltage battery (14.4V for example) then a 12V Reg and a 5V reg will do the trick nicely.

For regulators I often fall back on the 78XX series of 3 leg regulators (7805 for 5V and 7812 for 12V), depending on the power requirements will determine which style you need.

Here are some links for the regs.

Higher current devices are available and a heatsink will be required for full load.

TAIWAN SEMICONDUCTOR - TS7805CZ - IC, V REG +5.0V, 7805, TO-220-3 | CPC UK http://cpc.farnell.com/taiwan-semiconductor/ts7805cz/ic-v-reg-5-0v-7805-to-220-3/dp/SC10582

STMICROELECTRONICS - L7812CV - V REG +12V, 7812, TO-220-3 | CPC UK

2A variant of the 5V

STMICROELECTRONICS - L78S05CV - 5V, 2A Positive Voltage Regulator in TO-220-3 Package | CPC UK

Also this is an option - the 7" touchscreen for the Pi - no need for 12V then as the included board takes care of the supply for you!

Raspberry Pi 7” Touchscreen Display

Hi Vincent,

It would be easier to use a display which also requires the same voltage (5V), so you can run both the Pi and the display from a single 5V source. There are USB power sources (they have Li-Ion cells inside) with a USB output of 5V (there is an in-built DC-DC converter) which are intended for charging mobile phones. They can be used to power the Pi and display (you don't need 10V, the Pi and display are wired in parallel).

Also, the car reversing/backup displays are low-res, it may be hard to make out any text if it was used as a tablet. Some state a high res but actually output a standard def image which is unusable for text. About the minimum would something like the Pi 7" capacitive touch display, or some HDMI display perhaps.

Also, it would be good to check out some existing projects like this, for ideas, e.g. this URL: https://learn.adafruit.com/7-portable-raspberry-pi-multitouch-tablet/overview

You're right to be concerned about safety (that URL unfortunately does not mention battery safety, and I'm not sure I'd use a zip-tie around a Li-Po cell. But the rest of the info may be useful there), the off-the-shelf 5V USB power packs should be safe if some known reputable one is used (check the reviews on Amazon etc) from a reputable source. Make sure it can supply perhaps 2A or more (the Pi and display may consume this much).

Thanks for the answer shabaz.

Thanks for the quick answer.

No problems - shabaz mentions the same 7" Pi display in his reply - so 5V voltage requirements across the board makes life so much easier.

The temptation to make (possibly) cheaper displays work can sometimes work out more expensive, more complex and less successful in the long run.

I was thinking about the things you said about the display, but I watched the video from the ben heck show where they build the raspberrry pi portable (https://www.youtube.com/watch?v=Ko7eNx0zAuI ), and they say they used the lcd display they used in the portable atari build(https://www.youtube.com/watch?v=21qZKo0f280 ) , I watched that video and found the same screen on amazon (it has the same dimensions and looks identical), and it is way cheaper than the 7" display with a touchscreen, because I am still on a budget of course. And on the video the display was pretty easy to read. So i think i am going with that. If you think i am wrong please correct me.

Hi Vincent,

I think that's ok, it is really down to what resolution you're comfortable with. I just wasn't sure if that would be enough, but it could be fine as you say.

If you can aim to find a 5V one, then you can power everything from the USB 5V supply.