Yes. All of the negatives need to be connected together and connected to the negative terminal of the charger. Then connect the positives together and connect to the positive terminal of the charger. Make sure the batteries are fully charged before you start and you are using a 12V charger. You can start with one battery connected and add more batteries as you check that they are fully charged.
Sure you can and you will end up with 36 volts. Connect them in Parallel and you will have 12 volts.
Connect them together in Series. Connect the negative post of one battery to the positive post of the other battery. Then connect the negative charger cable to one negative battery post and the positive to the positive post of the other battery.
To measure voltage be in parallel with the battery. Series would measure current. Parallel measures potential.
Yes, the amps stay the same but the voltage doubles. If you connect in parallel the volts stay the same and the amps double.
You would need a 24 volt charger. Connect them in parallel and you can charge them both with a 12 volt charger. Or disconnect them and charge each one separately.
Yes, series and parallel connection of batteries is possible. When connected in series Voltage increases. In parallel, Current increases but voltage is constant.
Depends on how you connect them together. Connected them in a series and you will have 18 volts. Connected them in parallel and you will still have 9 volts just double the capacity of 1 battery. Click the link to see these 2 connections.
Connect the positive + red charger cable to the positive + red battery post. Then connect the negative - black charger cable to the engine somewhere. Most engines have something metal sticking up that you can connect to. Do not connect the negative charge cable to the negative battery post, always connect it to the engine.
Use a special charger, such as an RV or boat charger, that has multiple outputs (best). Connect the two batteries in series, and use a 24V charger (ok, if the two batts are exactly the same). Connect the two batteries in parallel and use a standard 12V charger ( worst choice, one battery tends to hog the current, and they receive unequal charges). See the links for a dual-output charger I Googled.
If you connect two transistors parallel it will heat up and be damaged.
Connect the positive (+) Red cable from the charger to the positive (+) post of the battery. Now connect the negative (-) Black cable to a metal part of the engine. Do not connect to negative battery post. Plug the charger in. Unplug the charger before removing the cables. Disconnect the negative cable first.
connect the charger and on it