I am not quite sure what you are asking. Are you looking for a recommendation for a specific battery?
When putting two batteries in parallel, it is best to have them as close to identical as possible. That means the same style and model, from the same manufacturer, and the same age. You won't be able to match the age of your existing battery, but if you can get an otherwise identical battery, that is the thing to do. If not, you will be better off with two new ones.
If you do go with two new ones, consider using 6 volt golf cart batteries in series. Trojan, US Battery, Interstate, and some others have 6V batteries rated at around 220 to 240 amp-hours, and also some larger ones, but the larger ones get pricey.
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