You cannot have one battery. You can have one cell. A battery is two or more cells in one unit. Example: your car has a six cell battery. The symbol for a cell is a short vertical line with a longer vertical line next to it.

Usually only 1 battery +|I-

I think we need more context here. Is the circuit just one battery and nothing else? Or is it one battery with two loads in parallel? If you only have one component in a circuit, it wouldn't make any sense to connect in series or parallel as those are different ways to connect two or more components to each other. But if you have two loads, you can absolutely connect those to each other in series or in parallel and then connect one battery to the circuit. The general circuit diagram for a battery is two parallel line segments with the anode (positive terminal) depicted slightly longer than the cathode (negative terminal) and the line segments perpendicular to the lines representing the wires.

When a question asks you to draw a "battery" in a parallel circuit, it typically refers to a single battery unless otherwise specified. The term "battery" is often used generically, even if multiple batteries are involved in a circuit, but it usually implies one battery unless the context or question suggests otherwise. The symbol for one battery is typically a pair of long and short parallel lines. The longer line represents the positive terminal, and the shorter line represents the negative terminal. In some diagrams, you may see multiple batteries connected in parallel, which would involve multiple battery symbols, each with its own positive and negative terminals, but for a single battery in a parallel circuit, you would use just one such symbol. In summary, unless the question specifies otherwise, drawing one battery usually means you draw the standard battery symbol with a long line (positive terminal) and a short line (negative terminal). The other components in the parallel circuit—such as resistors or light bulbs—would then be connected across the battery's terminals. Visit https://electricityforum.com to get more info.