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I’m planning to build a small walking robot using a Raspberry Pi Zero 2 W.
The robot will have 9 servo motors (9g SG90), controlled via a PCA9685 servo driver.

Power is supplied via a battery pack with 5V/3A outputs.

My question is:

Do I need two separate battery packs — one for the Raspberry Pi and one for the servos —
or can I power both from the same battery source?

Can I simply try it with one source, or would I risk damaging the Raspberry Pi if the servos draw too much current and the Pi doesn’t get enough?

Also, please note: I can’t power the Raspberry Pi via its USB port because that port is already used by a gamepad dongle.

stofl
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Each SG90 servo can draw ~650-700 mA stall current, though typical movement might use 100–300 mA.

With 9 servos, the total worst-case current draw could exceed 2A — especially during startup or heavy load. When the servos all move at once, the voltage may momentarily dip.

The Raspberry Pi Zero 2 W is sensitive to low voltage and may crash, freeze, or reboot if the voltage drops below ~4.7V. If space/weight is not a big issue, go with 2 separate packs — it’s more reliable and protects your Pi.

If you must use 1 battery,use a 5V 3A buck converter with filtering, add capacitors,Power the Pi through GPIO, not USB. Here is a project that features 9 SG90 servos. You can get some idea from it too.

tepalia
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There should be no need for multiple power packs.
I normally power 2 servos from the Pi 5 V (admittedly using mains power pack).
The current drawn by these small servos is quite low (typically ~100 mA) provided you avoid stalling the motors - which is poor for any motor.

You ask "would I risk damaging the Raspberry Pi if the servos draw too much current and the Pi doesn’t get enough" there is absolutely no risk of damaging a Pi from running on low voltage.

You don't appear to understand circuit theory; each device will draw the power it needs.
Provided the power supply can maintain the output voltage there wiil be no issue, so the real question is what are you using to convert the battery into a 5 v supply.

You also say "I can’t power the Raspberry Pi via its USB port" - the Pi has one USB port and one power port which can only supply power.
the Pi Zero has a very primitive power system, no protection and ALL 5V pins (including USB) are connected (in violation of USB specs).

Milliways
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You will not damage the Pi but the SD card can get corrupted.

If you have nine SG90 and they draw current at the same time and your battery pack (5v/3A) has a low max current draw (C) it could be an issue.

C-rate is a number that you have on battery packs and that is the max current you can load the battery pack.

Example: if you have a 5C and 5v/3A then you can load the battery with 5 times 3 Ampere = 15 A without damaging the battery.

And from what I can find about the SG90 servo it typically consumes around 550 mA during normal operation, but can draw up to 750 mA at stall. So if all nine SG90 stalls you will run into trouble.

MatsK
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