Upvote:1
Your new Indian passport will have old passport number (on the address page, at the bottom). Old passport will be canceled by cancel stamp on first page and it will be punched so that it can not be used in any machine readable device.
However, you HAVE to carry your old passport along with new one (specially when it has ongoing visa). Your ongoing visa will still be valid even if you renew your passport. It doesn't matter if you have entry stamps in old passport or new, as far as you have valid passport and valid visa, you can travel to respective country.
At the immigration gate, just present your ALL passports (new + old) to the officer and you are good to go.
Upvote:2
As long your passport is valid during your departure, you can renew it in India. You can apply for the renewal of the existing passport up to a year prior to the current passportβs expiry.
However, I strongly recommend carrying both passports with you while coming back to Germany. If custom control questions on your stamp, you can clearly show them the old one and the renewed one.
You can do online before visiting India too and then be there on time.